Related rates

Calculus can be applied in the typical day to day life of every person, which is why, it is important to study the different concepts under this branch of mathematics. Last chapter, we have discussed everything you need to know about Derivatives. We learned its definition, and we also learned how to find the derivative of a given function.

In this chapter, we will put to use our knowledge and practice from the previous lesson by discussing the applications of differential calculus. There are various real life applications of deriving functions. One example is that it can be used to compute for the rate of measure. It can also be used to find errors and make approximations. It can also be used to identify whether or not a function is increasing or decreasing. Derivation can also be used to compute for the maxima and minima of a given mathematical model.

This chapter has seven sections. In the first part of the chapter, we will look at the position velocity acceleration. Based from our previous lesson, we know that whenever we try to find the derivative of a function, we are actually looking for the instantaneous rate of change of that function. We will use this knowledge to study about the relationship of the position, velocity and the acceleration of a particle. We will also have a number of exercises that will deal with linear motion to help us understand how derivatives can help us for this particular topic.

In the second part of this chapter, we will look at maximization, minimization, and optimization. Optimization is simply the process where you find a value that would maximize or minimize the value of a certain function. We will have a more in depth discussion on the different applications of optimization in the fourth section of this chapter.

For the third part, we will study how to sketch different curves. We will also learn how to identify and locate an inflection point and intervals of concavity. The inflection point is basically a point in a curve where the curvature changes its direction. These two are used in the First Derivative Test and Second derivative test. We will also look into the definition of impossible limits and the L’Hospital’s Rule.

For the last three parts Chapter 3, we will discuss about related rates, Mean Value Theorem and linear approximation or tangent line approximation. The discussion about these three topics will help you solve word problems.

Related rates

Related rates come in handy when we have two related quantities and one of their rates of change is much harder to find than the other one. For example, look at the figure below, you can see that it is difficult to find the rate of change in radius of the balloon while it is being pumped up. However, the rate of change in volume of the balloon can be easily found if we know the air flow rate of the pump. Therefore, the work left with us is just to find the equation that relates the two related quantities, and then use the Chain Rule to differentiate both sides with respect to time.



Note: Problem Solving Strategy
1. If possible, draw a diagram to help visualize the problem.
2. Express the given rates (look for units with time in the denominator).
3. Express the asking rate (look for phrases such as “how fast”, “at what rate”, “find the rate”, etc.).
4. Write an equation that relates the various quantities of the problem.
5. Differentiate both sides of the equation, with respect to time, using the Chain Rule.
6. Substitute the given information into the differential equation and solve for the asking rate.
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Related rates

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