Identifier: Derivatives Inside Derivatives

Unfortunately, there is not an order of operations for derivatives that you can follow to tell you what derivative to do first. So, being able to identify your primary derivative rule, the rule you want to start with is crucial.

I always tell students to squint your eyes and when you look down at your problem what overall “shape” does it have. You don’t want to dive into the details, you want to pull yourself back and look at the problem overall. So overall, what does your problem look most like? This tells us the primary derivative rule we need to start applying. This allows us to then break that big problem down into bite-size chunks, and that is when we dive further into the details of the problem.

These are the overall shapes you want to be able to identify to help you determine the derivative rule.

Overall Shape when you squint your eyes.

Primary Derivative Rule

Example

y = (                    ) (                    )

y = ( SOMETHING ) ( SOMETHING )

 

Something inside a set of parentheses multiplied by something else in a set of parentheses.

Product Rule:

f g + g f

 

f ( x ) = ( 5 x 3 45 x 2 + 35 x ) 6 ( 5 x 4 + 3 x 2 ) 7

 

Primarily this is two chunks being multiplied.

y = (                 ) (                 )

y = ( SOMETHING ) ( SOMETHING )

 

Something divided by Something.

Quotient Rule:   ( low ) ( dhi ) ( hi ) ( dlow ) ( low ) 2

f ( x ) = ( 3 x 3 6 x + 9 ) 4 ( 5 x 4 + 3 x 2 ) 3

 

Primarily this is two chunks being divided.

f ( x ) = (                 ) Power

f ( x ) = ( SOMETHING ) Something

 

Something inside of something.

A function inside another function.

Chain Rule:

( DIN )( DOUT )

y = ( 3 x 3 6 x + 9 5 x 4 + 3 x 2 ) 5

Primarily this is an equation inside another equation.

Special cases

You have to have the special case options memorized to be able to identify them.

Like we talked about when we were learning all of these special case derivatives, once it is more than just a basic x inside the, it is a chain rule.

f ( x ) = ln ( sin ( x ) )

In this example the primary rule is the chain rule. The natural log special case acting as the outside has the sine function inside it.

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