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January 27, 2020

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### Section 3-9 : Chain Rule

26. Differentiate $$h\left( z \right) = {\tan ^4}\left( {{z^2} + 1} \right)$$ .

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Hint : Sometimes the Chain Rule will need to be done multiple times before we finish taking the derivative.
Start Solution

This problem will require multiple uses of the Chain Rule and so we’ll step though the derivative process to make each use clear. Also, recall that,

${\tan ^4}\left( x \right) = {\left[ {\tan \left( x \right)} \right]^4}$

Here is the first step of the derivative and we’ll need to use the Chain Rule in this step.

$h'\left( z \right) = 4{\tan ^3}\left( {{z^2} + 1} \right)\frac{d}{{dz}}\left[ {\tan \left( {{z^2} + 1} \right)} \right]$ Show Step 2

As we can see the derivative from the previous step will also require the Chain Rule.

The derivative is then,

$h'\left( z \right) = 4{\tan ^3}\left( {{z^2} + 1} \right){\sec ^2}\left( {{z^2} + 1} \right)\left( {2z} \right) = \require{bbox} \bbox[2pt,border:1px solid black]{{8z{{\tan }^3}\left( {{z^2} + 1} \right){{\sec }^2}\left( {{z^2} + 1} \right)}}$