# Evaluating inverse trigonometric functions

##### Intros
###### Lessons
1. Application of the Cancellation Laws

Introduction to Evaluating Inverse Trigonometric Functions

##### Examples
###### Lessons
1. Understanding the Use of Inverse Trigonometric Functions

Find the angles for each of the following diagrams.

2. Find the angle for the following isosceles triangle.

1. Determining the Angles in Exact Values by Using Special Triangles

Find the angles for each of the following diagrams in exact value.

2. Application of the Cancellation Laws

Solve the following inverse trigonometric functions:

1. $\sin (\sin^{-1} 0.5)$
2. $\cos^{-1} (\cos \frac{\pi}{4})$
3. $\sin^{-1} (\sin \frac{3\pi}{4})$
3. Solving Expressions With One Inverse Trigonometry

Solve the following inverse trigonometric functions:

1. $\cos^{-1} \frac{1}{2}$
2. $\sin^{-1} \frac{1}{2}$
4. Evaluating Expressions With a Combination of Inverse and Non-Inverse Trigonometry

Solve the following inverse trigonometric functions:

1. $\sin (\cos^{-1} \frac{\sqrt 3}{2})$
2. $\cos (\sin^{-1} \frac{2}{3})$
3. $\cos (2\tan^{-1} \sqrt 2)$
4. $\cos (\sin^{-1} x)$
5. Special Cases: Evaluating Functions With Numbers Outside of the Restrictions

Solve the following inverse trigonometric functions:

1. $\cos^{-1} (\cos \frac{3\pi}{2})$
2. $\sin^{-1} (\sin \frac{5\pi}{2})$

## Introduction to Evaluating Inverse Trigonometric Functions

Evaluating inverse trigonometric functions is a crucial skill in advanced mathematics. This topic builds upon your knowledge of trigonometric functions and their graphs, taking your understanding to the next level. The introduction video provides a comprehensive overview of inverse trigonometric functions, serving as a foundation for mastering this concept. It's essential to have a solid grasp of basic trigonometry before diving into this subject. Inverse trigonometric functions, also known as arcfunctions, allow us to find angles when given trigonometric ratios. Understanding these functions is vital for solving complex equations and real-world applications in fields like physics and engineering. The video will guide you through the process of evaluating these functions, introducing key concepts such as domain restrictions and cancellation laws. By the end of this section, you'll be equipped with the tools to confidently work with inverse trigonometric functions and apply them to various mathematical problems.

## Understanding Trigonometric Cancellation Laws

Hey there! Let's dive into the fascinating world of simplify trigonometric expressions. Imagine these laws as magical rules that can simplify trigonometric expressions. We'll explore six of these laws and see how they can make our math lives easier!

First, let's recap the six cancellation laws we derived earlier:

1. sin(arcsin(x)) = x, for -1 x 1
2. cos(arccos(x)) = x, for -1 x 1
3. tan(arctan(x)) = x, for all real x
4. arcsin(sin(x)) = x, for -π/2 x π/2
5. arccos(cos(x)) = x, for 0 x π
6. arctan(tan(x)) = x, for -π/2 < x < π/2

Now, you might be wondering, "How can we use these laws in real-life math problems?" Well, these laws are super helpful when we need to simplify trigonometric expressions or solve equations involving trigonometric functions and their inverses.

Let's look at some examples to see when cancellation can occur:

Example 1: Suppose we have sin(arcsin(0.5)). Using the first law, we can immediately simplify this to 0.5. It's like the sin and arcsin cancel each other out, leaving us with the value inside.

Example 2: If we encounter cos(arccos(3/2)), we can apply the second law and simplify it to 3/2. Again, the cos and arccos cancel out.

But here's the catch cancellation doesn't always work! We need to be careful about the domain restrictions mentioned in the laws. Let's see when cancellation can't occur:

Example 3: Consider arcsin(sin(2π)). We can't apply the fourth law here because 2π is outside the range -π/2 x π/2. In this case, we'd need to use other trigonometric identities to simplify the expression.

Example 4: For arccos(cos(3π/4)), we can't directly cancel because 3π/4 is outside the range 0 x π specified in the fifth law. We'd need to adjust the angle first before applying the law.

These laws are like secret weapons in your trigonometry toolkit. They can save you time and effort when solving complex problems. But remember, always check the domain restrictions before applying them!

Here's a pro tip: When you're working with composite functions like sin(arcsin(x)) or arccos(cos(x)), think about whether the inner function's output falls within the outer function's domain. If it does, you can often apply a cancellation law.

Practice using these laws with different expressions. The more you work with them, the more intuitive they'll become. And don't worry if it feels tricky at first that's totally normal! With time and practice, you'll be cancelling like a pro.

Remember, these cancellation laws are just one part of the bigger trigonometry picture. They work hand in hand with other trigonometric identities and concepts. So, keep exploring and connecting the dots between different trigonometric ideas. Before you know it, you'll be seeing patterns and simplifications everywhere in your trig problems!

## Evaluating Single Inverse Trigonometric Expressions

Inverse trigonometric functions, such as inverse cosine (arccos) and inverse sine function (arcsin), present unique challenges in mathematical problem-solving. These functions are the reverse operations of their trigonometric counterparts, allowing us to find angles when given ratio values. When dealing with expressions that involve a single inverse trigonometric functions, it's crucial to understand their properties and limitations to effectively evaluate them.

The primary challenge with inverse trigonometric functions lies in their restricted domains and ranges. For instance, the inverse sine function (arcsin) also has a domain of [-1, 1] but a range of [-π/2, π/2]. These constraints are essential to keep in mind when solving problems involving these functions.

To approach problems with single inverse expressions, consider the following strategies:

1. Identify the specific inverse function (e.g., arccos, arcsin) and recall its domain and range.
2. Examine the input value within the inverse function to ensure it falls within the valid domain.
3. If the expression involves algebraic manipulations, simplify it before applying the inverse function.
4. Use the properties of inverse functions to simplify complex expressions when possible.
5. Consider the context of the problem to determine if additional steps, such as angle conversion, are necessary.

Let's walk through a step-by-step example to illustrate these strategies:

Example: Evaluate arccos(1/2)

1. We're dealing with the inverse cosine function (arccos).
2. The input value 1/2 is within the domain of arccos [-1, 1].
3. No simplification is needed in this case.
4. Recall that arccos(1/2) is a common angle in the unit circle, corresponding to 60 degrees or π/3 radians.
5. Therefore, arccos(1/2) = π/3 radians or 60 degrees.

For a more complex example, consider: Evaluate arcsin(3/2)

1. We're working with the inverse sine function (arcsin).
2. The input 3/2 is within the domain of arcsin [-1, 1].
3. No simplification is required.
4. Recognize that 3/2 is the sine of a common angle in the unit circle.
5. arcsin(3/2) corresponds to 60 degrees or π/3 radians.

When dealing with more complex expressions, such as arccos(2x - 1), follow these steps:

1. Identify that we're working with the inverse cosine function.
2. Set up an equation: y = arccos(2x - 1)
3. Apply cosine to both sides: cos(y) = 2x - 1
4. Solve for x: x = (cos(y) + 1) / 2
5. Remember that y is restricted to [0, π] due to the range of arccos.

In conclusion, evaluating single inverse trigonometric expressions requires a solid understanding of their properties, domains, and ranges. By following the strategies outlined above and practicing with various examples, you can develop the skills needed to tackle these challenging problems effectively. Remember to always consider the context of the problem and be mindful of the limitations of inverse trigonometric functions to arrive at accurate solutions.

## Solving Expressions with Mixed Trigonometric Functions

When approaching expressions that involve two different trigonometric functions, such as sine and inverse cosine, it's crucial to understand the unique challenges they present compared to expressions with matching functions. These mixed trigonometric function problems require a deeper understanding of function relationships and often necessitate a more strategic approach to solving.

Let's begin by examining the difference between expressions with matching functions and those with mixed functions. When dealing with matching functions, such as sin(sin¹(x)), the inverse function typically cancels out the inner function, simplifying the expression. However, with mixed functions like sin(cos¹(x)), this direct cancellation doesn't occur, making the problem more complex.

To tackle expressions with mixed trigonometric functions, it's essential to understand the relationships between different trigonometric functions. For instance, sine and cosine are related through the Pythagorean identity: sin²θ + cos²θ = 1. This relationship can be crucial when solving problems involving these functions.

Let's walk through an example to illustrate the process. Consider the expression: sin(cos¹(x))

Step 1: Visualize the problem. Imagine a right triangle where the cosine of an angle is x. We're trying to find the sine of this same angle.

Step 2: Use the Pythagorean identity. If cos θ = x, then sin²θ = 1 - x².

Step 3: Take the square root of both sides. sin θ = (1 - x²)

Step 4: Consider the domain. Since we're dealing with an inverse cosine function, x must be between -1 and 1. This ensures that (1 - x²) is always non-negative, so we don't need to consider the negative root.

Therefore, sin(cos¹(x)) = (1 - x²) for -1 x 1.

This example demonstrates the importance of understanding function relationships. By recognizing the connection between sine and cosine through the Pythagorean identity, we were able to solve a problem that initially seemed complex.

Another common type of mixed trigonometric expression involves tangent and inverse sine or cosine. For instance, consider tan(sin¹(x)):

Step 1: Visualize a right triangle where sin θ = x.

Step 2: In this triangle, the opposite side is x, and the hypotenuse is 1 (since sin θ = opposite / hypotenuse = x / 1).

Step 3: Use the Pythagorean theorem to find the adjacent side: adjacent² = 1² - x² = 1 - x²

Step 4: Recall that tan θ = opposite / adjacent. In this case, that's x / (1 - x²).

Therefore, tan(sin¹(x)) = x / (1 - x²) for -1 < x < 1.

These examples highlight the importance of visualizing the problem, using known trigonometric identities, and understanding the relationships between different trigonometric functions. When approaching mixed trigonometric expressions, it's often helpful to:

1. Identify the outer and inner functions and their relationships.
2. Visualize the problem using right triangles or the unit circle.
3. Apply relevant trigonometric identities.
4. Consider the domains of trigonometric functions involved.
5. Simplify the expression step by step.

By mastering these techniques and developing a strong grasp of function relationships, you'll be well-equipped to tackle even the most challenging mixed trigonometric expressions. Remember, practice is key to becoming proficient in solving these types of problems. As you work through various examples, you'll begin to recognize patterns and develop intuition for the most effective problem-solving strategies.

## Applying Trigonometric Identities in Inverse Function Evaluation

Trigonometric identities are powerful tools in mathematics, especially when dealing with complex expressions involving inverse trigonometric functions. One particularly useful identity is the cosine double angle formula, which can simplify seemingly complicated expressions. In this section, we'll explore how to apply such identities, using the example of cos(2tan¹(2)) to illustrate the process.

Before diving into our example, it's crucial to refresh our memory on some key trigonometric identities. The cosine double angle formula states that:

cos(2θ) = cos²θ - sin²θ = 2cos²θ - 1 = 1 - 2sin²θ

Additionally, we should recall the Pythagorean identity:

sin²θ + cos²θ = 1

Now, let's tackle our example: cos(2tan¹(2)). At first glance, this expression might seem daunting, but by simplifying trigonometric expressions and some clever substitutions, we can simplify it significantly.

Step 1: Let θ = tan¹(2). This means that tan θ = 2.

Step 2: Apply the cosine double angle formula:

cos(2tan¹(2)) = cos(2θ) = 2cos²θ - 1

Step 3: Now, we need to find cos²θ. We can do this using the tangent value we know and the Pythagorean identity.

Since tan θ = 2, we can write: tan²θ = 2

Using the identity tan²θ = sin²θ / cos²θ, we get:

2 = sin²θ / cos²θ

Cross-multiplying: 2cos²θ = sin²θ

Substituting this into the Pythagorean identity:

sin²θ + cos²θ = 1

2cos²θ + cos²θ = 1

3cos²θ = 1

cos²θ = 1/3

Step 4: Now that we have cos²θ, we can substitute this back into our cosine double angle formula:

cos(2tan¹(2)) = 2cos²θ - 1 = 2(1/3) - 1 = 2/3 - 1 = -1/3

Thus, we've successfully evaluated cos(2tan¹(2)) to be -1/3.

This example demonstrates the power of simplifying trigonometric expressions. By breaking down the problem into manageable steps and applying known identities, we can solve problems that initially appear challenging.

It's important to note that success in these types of problems often relies on recalling and correctly applying previously learned concepts. Regularly reviewing fundamental trigonometric identities, such as the double angle formulas, Pythagorean identity, and relationships between trigonometric functions, is crucial for tackling advanced problems.

Some other important identities to remember include:

- Sin(A+B) = sinA cosB + cosA sinB

- Cos(A+B) = cosA cosB - sinA sinB

- Tan(A+B) = (tanA + tanB) / (1 - tanA tanB)

These identities, along with their variations for subtraction and half angles, form a comprehensive toolkit for solving a wide range of trigonometric problems.

## Evaluating Expressions with Variables

Solving inverse trigonometric expressions with variables requires a different approach compared to working with specific numbers. When dealing with variables, it's crucial to understand the domain and range of inverse trigonometric functions to ensure accurate solutions. Let's explore the process and considerations involved in evaluating these expressions.

First, it's essential to recognize that inverse trigonometric functions have restricted domains and ranges. For example, the domain of arccos(x) is [-1, 1], and its range is [-π/2, π/2]. Similarly, arccos(x) has a domain of [-1, 1] and a range of [0, π]. Understanding these limitations is vital when working with variables.

When solving expressions with variables, start by identifying the inverse trigonometric function involved. Then, consider the possible values the variable can take within the function's domain. For instance, if you're dealing with arcsin(x), you know that x must be between -1 and 1, inclusive.

Next, apply algebraic manipulations to isolate the variable within the inverse trigonometric function. This step often involves using trigonometric identities or properties of inverse functions. For example, if you have an equation like sin(arccos(x)) = y, you can simplify it using the identity sin(arccos(x)) = (1-x²).

When working with composite functions involving inverse trigonometry and variables, be cautious about the order of operations. Remember that arcsin(sin(x)) x for all x, as the range of arcsin limits the possible outputs.

Let's consider an example: Solve for x in the equation arctan(2x) + arctan(x) = π/4. To approach this, we can use the tangent addition formula: tan(A + B) = (tan A + tan B) / (1 - tan A tan B). Applying this to our equation, we get: tan(arctan(2x) + arctan(x)) = tan(π/4) = 1. This leads to (2x + x) / (1 - 2x²) = 1, which simplifies to 3x = 1 - 2x², or 2x² + 3x - 1 = 0. Solving this quadratic equation gives us x = 1/2 or x = -1, but we must check these solutions against the domain of arctan.

Another important consideration when dealing with variables in inverse trigonometric expressions is the possibility of multiple solutions. Unlike specific numerical inputs, variables can lead to multiple valid answers within the function's domain. Always verify your solutions by substituting them back into the original equation.

In conclusion, solving inverse trigonometric expressions with variables requires a solid understanding of domain and range, careful algebraic manipulation, and attention to the unique properties of these functions. By following these guidelines and practicing with various examples, you'll develop the skills needed to tackle complex problems involving inverse trigonometry and variables.

## Exception Cases in Trigonometric Cancellation

When working with inverse trigonometric functions, students often encounter general cancellation rules that simplify expressions. However, it's crucial to understand that there are exceptions to these rules, which can lead to incorrect solutions if not properly identified and addressed. In this section, we'll explore these exception cases, explain why they occur, and provide guidance on how to approach them correctly.

The most common cancellation rule for inverse trigonometric functions states that for any angle θ, sin(arcsin(θ)) = θ and cos(arccos(θ)) = θ. While this rule holds true in many cases, there are specific situations where it doesn't apply. These exceptions occur due to the restricted domains and ranges of inverse trigonometric functions.

One notable exception arises when dealing with the composition of sine and arcsine functions outside the range of [-1, 1]. For instance, consider the expression sin(arcsin(x)). The general cancellation rule would suggest that this simplifies to x. However, this is only true when -1 x 1. For values of x outside this range, the arcsine function is undefined, making the entire expression invalid.

Similarly, for cos(arccos(x)), the cancellation only works within the domain of arccos, which is [-1, 1]. Any value of x outside this range will result in an undefined expression. It's essential to always check the domain of the inner function before applying cancellation rules.

Another exception occurs with tan(arctan(x)). While this generally simplifies to x, it's important to note that the range of arctan is (-π/2, π/2). For values of x that would result in angles outside this range, the simple cancellation doesn't hold true. In such cases, the correct approach is to consider the periodicity of the tangent function and adjust the result accordingly.

To identify these exception cases, always follow these steps:

1. Determine the domain and range of the inner inverse trigonometric function.
2. Check if the argument of the inverse function falls within its valid domain.
3. Consider the range of the outer trigonometric function and how it relates to the inner function's output.
4. Be aware of any restrictions or periodicity that might affect the final result.

Let's examine a specific example to illustrate these concepts. Consider the expression sin(arcsin(2)). At first glance, one might be tempted to cancel out the sine and arcsine, resulting in 2. However, this would be incorrect. The value 2 is outside the domain of arcsin, which is [-1, 1]. Therefore, arcsin(2) is undefined, making the entire expression invalid.

In cases where simple cancellation doesn't work, the correct approach often involves breaking down the problem into steps and carefully considering the domains and ranges at each stage. For instance, when dealing with tan(arctan(x)) where x is very large, you might need to consider the principal value of arctan and then apply the tangent function, keeping in mind its periodicity.

Another important exception to be aware of involves the composition of different trigonometric functions, such as sin(arccos(x)) or cos(arcsin(x)). These expressions don't cancel out and require a different approach. In these cases, it's often helpful to use trigonometric identities or to visualize the problem geometrically to arrive at the correct solution.

By understanding these exception cases and approaching them methodically, you can avoid common pitfalls in trigonometric problem-solving. Always be vigilant about the domains and ranges of the functions involved, and don't hesitate to break down complex expressions into manageable steps. With practice, you'll develop a keen eye for identifying these special cases and handling them with confidence.

## Conclusion and Further Practice

In this article, we've explored the essential concepts of inverse trigonometric functions and their evaluation techniques. Understanding these functions is crucial for advanced mathematics and various real-world applications. We've covered key points such as domain restrictions, range, and the relationship between inverse and regular trigonometric functions. Mastering these concepts requires consistent practice and application. If you're still unsure about any aspect, we encourage you to revisit the introduction video for a comprehensive overview. To further solidify your understanding, try solving additional problems from textbooks or online resources. Consider exploring graphing calculators to visualize these functions and their properties. Remember, proficiency in inverse trigonometric functions will greatly benefit your mathematical journey, especially in calculus and physics. Don't hesitate to seek help from teachers or online forums if you encounter difficulties. With dedication and practice, you'll soon become confident in working with these important mathematical tools.

### Example:

Solving Expressions With One Inverse Trigonometry

Solve the following inverse trigonometric functions:

$\cos^{-1} \frac{1}{2}$

#### Step 1: Understanding the Problem

We are given an inverse trigonometric function, specifically the inverse cosine of $\frac{1}{2}$. Our goal is to find the angle whose cosine is $\frac{1}{2}$. This can be a bit tricky because our brains are more accustomed to dealing with direct trigonometric functions rather than their inverses.

#### Step 2: Introducing a Variable

To make the problem more manageable, we introduce a variable. Let's say that $\cos^{-1} \frac{1}{2} = x$. This means we are looking for an angle $x$ such that the cosine of $x$ is $\frac{1}{2}$. By doing this, we have converted our expression into an equation: $\cos^{-1} \frac{1}{2} = x$.

#### Step 3: Applying the Cosine Function

Next, we apply the cosine function to both sides of the equation. This gives us $\cos(\cos^{-1} \frac{1}{2}) = \cos(x)$. According to the properties of inverse trigonometric functions, $\cos(\cos^{-1} y) = y$ for $y$ in the range $[-1, 1]$. Since $\frac{1}{2}$ is within this range, we can simplify the left-hand side to $\frac{1}{2}$. Thus, we have $\frac{1}{2} = \cos(x)$.

#### Step 4: Solving for $x$

Now, we need to find the angle $x$ such that $\cos(x) =$\frac{1}{2}$. This is a standard trigonometric problem. We know from our knowledge of special triangles that$\cos(\pi/3) = $\frac{1}{2}$. Therefore, $x = \pi/3$.

#### Step 5: Verifying the Solution

To ensure our solution is correct, we can verify it by substituting $x = \pi/3$ back into the original inverse trigonometric function. We have $\cos^{-1} \frac{1}{2} = \pi/3$, which confirms that our solution is accurate.

#### Conclusion

By introducing a variable and applying the cosine function to both sides of the equation, we were able to convert the inverse trigonometric function into a more familiar form. This allowed us to solve for the angle $x$ and verify our solution. The key steps involved understanding the problem, introducing a variable, applying the cosine function, solving for $x$, and verifying the solution.

### FAQs

1. What are inverse trigonometric functions?

Inverse trigonometric functions, also known as arcfunctions, are the reverse operations of trigonometric functions. They allow us to find angles when given trigonometric ratios. Common inverse trigonometric functions include arcsin (inverse sine), arccos (inverse cosine), and arctan (inverse tangent).

2. What are the domains and ranges of inverse trigonometric functions?

The domains and ranges vary for each function:
- arcsin(x): Domain [-1, 1], Range [-π/2, π/2]
- arccos(x): Domain [-1, 1], Range [0, π]
- arctan(x): Domain (all real numbers), Range (-π/2, π/2)

3. How do you evaluate expressions with mixed trigonometric functions?

When evaluating expressions with mixed functions (e.g., sin(cos¹(x))), use trigonometric identities, visualize the problem using right triangles or the unit circle, and apply relevant relationships between functions. Often, breaking down the problem into steps and using known identities can simplify the process.

4. What are some common mistakes when using trigonometric cancellation laws?

Common mistakes include ignoring domain restrictions and applying cancellation laws incorrectly. For example, sin(arcsin(x)) = x only when -1 x 1. Always check the domain of the inner function and consider the range of the outer function before applying cancellation laws.

5. How can I improve my skills in evaluating inverse trigonometric functions?

1. Practice regularly with a variety of problems
2. Review and memorize key trigonometric identities
3. Use graphing calculators to visualize functions
4. Work on problems that combine different trigonometric concepts
5. Seek help from teachers or online resources when stuck

### Prerequisite Topics for Evaluating Inverse Trigonometric Functions

Understanding inverse trigonometric functions is a crucial skill in advanced mathematics, but it requires a solid foundation in several prerequisite topics. One of the most fundamental concepts is determining trigonometric functions given their graphs. This skill is essential because inverse trigonometric functions are essentially the reverse process of regular trigonometric functions, and understanding their graphical representations is key to evaluating them correctly.

Another important prerequisite is the ability to use tangent ratio to calculate angles and sides. This concept is directly related to inverse trigonometric functions, as the arctangent function is the inverse of the tangent function. Understanding how to work with tangent ratios provides a strong foundation for grasping inverse trigonometric concepts.

While it may seem unrelated at first, knowledge of distance and time related questions in linear equations can be beneficial. This algebraic skill helps in understanding the practical applications of inverse trigonometric functions, particularly in physics and engineering problems involving angles and distances.

Familiarity with solving expressions using 30-60-90 special right triangles is also crucial. These special triangles often appear in problems involving inverse trigonometric functions, and understanding their properties can simplify complex calculations.

The unit circle is a fundamental concept that ties closely to inverse trigonometric functions. It provides a visual representation of trigonometric relationships and is essential for understanding the domain and range of inverse trigonometric functions.

For those looking to apply inverse trigonometric functions in calculus, knowledge of integration using trigonometric identities is valuable. This skill often involves inverse trigonometric functions and helps in solving complex integration problems.

Understanding composite functions is also important, as inverse trigonometric functions are often composed with other functions in advanced problems. This algebraic concept helps in breaking down complex expressions involving inverse trigonometric functions.

For calculus students, familiarity with the derivative of inverse trigonometric functions is essential. This topic directly builds upon the evaluation of inverse trigonometric functions and is crucial for solving differential equations involving these functions.

Knowledge of double-angle identities can also be helpful when working with inverse trigonometric functions, as these identities often appear in complex trigonometric equations involving inverse functions.

Lastly, understanding graphing transformations of trigonometric functions provides insight into how inverse trigonometric functions behave graphically. This knowledge is crucial for visualizing and solving problems involving these functions.

By mastering these prerequisite topics, students will be well-prepared to tackle the challenges of evaluating inverse trigonometric functions and apply this knowledge in various mathematical and real-world contexts.

In this lesson, we will learn:

• Application of the Cancellation Laws
• Solving Expressions With One Inverse Trigonometry
• Evaluating Expressions With a Combination of Inverse and Non-Inverse Trigonometry
• Special Cases: Evaluating Functions With Numbers Outside of the Restrictions

Cancellation Laws:

$\sin^{-1} (\sin x) = x\;$, $-\frac{\pi}{2} \leq x \leq \frac{\pi}{2}$

$\sin (\sin^{-1} x) = x\;$, $-1 \leq x \leq 1$

$\cos^{-1} (\cos x) = x\;$, $0 \leq x \leq \pi$

$\cos (\cos^{-1} x) = x\;$, $-1 \leq x \leq 1$

$\tan^{-1} (\tan x) = x\;$, $-\frac{\pi}{2} \leq x \leq \frac{\pi}{2}$

$\tan (\tan^{-1} x) = x\;$, $-\infty$ < $x$ < $\infty$

Trigonometric Identity:

$\cos 2\theta = \cos^{2} \theta - \sin^{2} \theta$