The chain rule is a powerful tool used in the process of differentiation, especially for composite functions. Composite functions combine two or more functions, resulting in a new function known as a function of a function.

The formula for the chain rule is as follows:

**Chain rule formula:**

if *y* is a function of *u* and *u* is a function of *x*, then *dy/dx = dy/du * du/dx*.

**Function notation:**

if *f* is a function of *x*, then *f'(x)* = *f'(u)* * *du/dx*.

To better understand the chain rule, let's examine some examples:

**Example 1:**

If*y*=*u*² and*u*=*x*³, find*dy/dx*.**Example 2:**

If*y*= cos*u*and*u*= 2*x*, find*dy/dx*.

By applying the chain rule formula, we can easily solve for *dy/dx* in each example.

Sometimes, the given function may be in function notation and we are asked to differentiate it. In this case, the steps are similar:

- Differentiate the function with respect to
*x*to find*f'(x)*. - Substitute the value of
*u*into*f'(x)*to find*f'(u)*. - Differentiate
*u*with respect to*x*to find*du/dx*. - Substitute the values into the chain rule formula to find
*f'(x)*.

If the function given is not in the form *y* = *f*(*u*), we can use a different formula:

**Reverse chain rule formula:**

if *u* = *f*(*x*), then *f'(x)* = *dy/du * du/dx*.

For example:

**Example 3:**

Find the value of *dy/dx* at the point (*3*,*5*) on the curve *x* = 2*y* - *y*².

We can easily solve for *dy/dx* using the reverse chain rule formula by differentiating with respect to *y* and substituting the values into the formula.

The chain rule is also useful in the integration process, known as the reverse chain rule. The steps are:

- Identify the main function and break it down into its integral.
- Work backwards by taking the differentiated function back to its integral form.
- When differentiating to a power, bring down the power in front of
*x*and decrease the power by 1. - Substitute the values into the reverse chain rule formula and add a constant,
*c*, to the final answer.

- The chain rule simplifies differentiation of composite functions.
- The formula for the chain rule is
*dy/dx = dy/du * du/dx*. - The reverse chain rule is useful for integrating functions.
- Knowing when and how to use the chain rule is essential for differentiation and integration processes.

Understanding the chain rule allows for easier handling of complex functions. By applying the correct formula, you can effortlessly differentiate and integrate composite functions with confidence.

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