# Completing the Square: Unlock the Power of Quadratic Equations Master the art of completing the square to solve complex quadratic equations, find parabola vertices, and convert to vertex form. Boost your algebra skills and tackle real-world math problems with confidence.

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Now Playing:Completing the square– Example 0
Intros
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1. What is "COMPLETING THE SQUARE"?
Examples
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1. Recognizing a Polynomial that Can Be Written as a Perfect Square
Convert the following expressions into perfect squares, if possible:
1. ${x^2} + 6x + {3^2}$ =
${x^2} - 6x + {\left( { - 3} \right)^2}$ =

2. ${x^2} + 20x + 100$ =
${x^2} - 20x + 100$ =
${x^2} - 20x - 100$ =

Practice
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Notes
perfect squares:
• ${\left( {x + a} \right)^2} = {x^2} + 2ax + {a^2}$
• ${\left( {x - a} \right)^2} = {x^2} - 2ax + {a^2}$
• completing the square: adding a constant to a quadratic expression to make it a perfect square
Concept

## Introduction to Completing the Square

Completing the square is a fundamental technique in algebra, essential for solving quadratic equations and graphing quadratic functions. Our introduction video provides a clear, step-by-step explanation of this concept, making it accessible to students of all levels. This method transforms a quadratic expression into a perfect square trinomial, allowing for easier manipulation and analysis. By mastering completing the square, students gain a powerful tool for simplifying complex equations, finding roots, and identifying key features of quadratic graphs. It's particularly useful in determining the vertex of a parabola, which is crucial in many real-world applications. The technique also bridges the gap between factoring and the quadratic formula, offering an alternative approach when traditional methods fall short. Understanding completing the square not only enhances problem-solving skills in algebra but also provides a deeper insight into the structure of quadratic expressions, laying a solid foundation for more advanced mathematical concepts.

Example

Recognizing a Polynomial that Can Be Written as a Perfect Square
Convert the following expressions into perfect squares, if possible:
${x^2} + 6x + {3^2}$ =
${x^2} - 6x + {\left( { - 3} \right)^2}$ =

#### Step 1: Identify the Terms

First, we need to identify the terms in the given polynomial expressions. For the first expression, we have:

• First term: $x^2$
• Middle term: $6x$
• Last term: $3^2$
For the second expression, we have:
• First term: $x^2$
• Middle term: $-6x$
• Last term: $(-3)^2$

#### Step 2: Check the Squared Terms

Next, we need to check if the first and last terms are already in squared form. In both expressions, the first term is $x^2$ and the last term is a squared number ($3^2$ and $(-3)^2$). This means they are already in the correct form.

#### Step 3: Verify the Middle Term

To ensure the polynomial can be written as a perfect square, we need to verify the middle term. The middle term should be $2$ times the product of the square roots of the first and last terms. Let's check this for both expressions:

• For ${x^2} + 6x + {3^2}$:
• First term without square: $x$
• Last term without square: $3$
• Middle term should be: $2 \times x \times 3 = 6x$
• For ${x^2} - 6x + {\left( { - 3} \right)^2}$:
• First term without square: $x$
• Last term without square: $-3$
• Middle term should be: $2 \times x \times (-3) = -6x$
Since the middle terms match the given expressions, we can proceed to the next step.

#### Step 4: Write the Perfect Square

Now that we have verified the terms, we can write the expressions as perfect squares:

• For ${x^2} + 6x + {3^2}$, the perfect square is $(x + 3)^2$.
• For ${x^2} - 6x + {\left( { - 3} \right)^2}$, the perfect square is $(x - 3)^2$.

#### Step 5: Conclusion

By following these steps, we have successfully converted the given polynomial expressions into perfect squares. This method can be applied to any similar polynomial to determine if it can be written as a perfect square.

FAQs

1. What is completing the square?

Completing the square is an algebraic technique used to transform a quadratic expression into a perfect square trinomial. It's particularly useful for solving quadratic equations, finding the vertex of a parabola, and converting quadratic functions to vertex form.

2. When should I use the completing the square method?

You should use completing the square when you need to find the vertex of a parabola, convert a quadratic function to vertex form, or solve a quadratic equation that's difficult to factor. It's also helpful in deriving the quadratic formula.

3. What are the steps to complete the square?

The basic steps are: 1) Group the x² and x terms. 2) Factor out the coefficient of x² if it's not 1. 3) Take half the coefficient of x and square it. 4) Add and subtract this term inside the parentheses. 5) Factor the perfect square trinomial. 6) Simplify the remaining terms.

4. How does completing the square help in graphing parabolas?

Completing the square converts a quadratic function to vertex form, a(x-h)² + k, where (h,k) is the vertex of the parabola. This form immediately reveals the parabola's vertex, axis of symmetry, and direction of opening, making it much easier to graph.

5. What are common mistakes to avoid when completing the square?

Common mistakes include forgetting to halve the coefficient of x before squaring, neglecting to add and subtract the same term to maintain equation balance, incorrectly factoring the perfect square trinomial, and mishandling negative coefficients. Always double-check your work and practice regularly to avoid these errors.

Prerequisites

Understanding the process of completing the square is crucial in algebra, but it's essential to grasp several prerequisite concepts first. One fundamental skill is factoring perfect square trinomials, which forms the basis of the completing the square method. This technique allows you to recognize and manipulate expressions in the form (a + b)² or (a - b)².

Before diving into completing the square, it's beneficial to be familiar with solving quadratic equations using the quadratic formula. This knowledge provides a solid foundation for understanding different approaches to quadratic equations. Additionally, graphing quadratic functions is crucial as it helps visualize the relationship between the algebraic and geometric representations of quadratics.

The vertex form of quadratic equations is closely related to completing the square. Understanding this form, y = a(x-p)² + q, is essential as completing the square often involves converting from general to vertex form. This connection extends to graphing reciprocals of quadratic functions, which builds upon your understanding of quadratic graphs.

Recognizing the characteristics of quadratic functions is vital when completing the square, as it helps you interpret the results and understand their significance. Another crucial skill is the ability to factor by taking out the greatest common factor, which is often a preliminary step in the completing the square process.

The core of the topic lies in converting from general to vertex form by completing the square. This skill directly applies the concept and is essential for mastering the technique. While it may seem unrelated, using models to add and subtract fractions can help in visualizing the process of completing the square, especially when dealing with fractional coefficients.

Finally, the ultimate goal is often solving quadratic equations by completing the square. This skill brings together all the prerequisite knowledge, allowing you to approach quadratic equations from a powerful geometric perspective.

By mastering these prerequisite topics, you'll be well-prepared to tackle the concept of completing the square with confidence and a deeper understanding of its applications in algebra and beyond.