Calculus AB : Use Derivatives of Trig Functions

Study concepts, example questions & explanations for Calculus AB

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Example Questions

Example Question #1 : Use Derivatives Of Trig Functions

Which of the following is the derivative of ?

Possible Answers:

Correct answer:

Explanation:

Recall that the function .  Knowing this, we can use the quotient rule to find the derivative.

 

                                                   (Pythagorean Identity)

                                                    

Example Question #2 : Use Derivatives Of Trig Functions

Which of the following is the derivative of ?

Possible Answers:

Correct answer:

Explanation:

 

 

 

 

 

 

 

 Recall that 

 

 

                     

Example Question #3 : Use Derivatives Of Trig Functions

Which of the following is the derivative of ?

Possible Answers:

Correct answer:

Explanation:

Recall that 

 

                

Example Question #4 : Use Derivatives Of Trig Functions

What is the derivative for ?

Possible Answers:

Correct answer:

Explanation:

Recall that .  We are able to use the quotient rule to find the derivative now.

 

             (Pythagorean Identity)

               

 

 

Example Question #5 : Use Derivatives Of Trig Functions

True or False: We use the Chain Rule to find the derivatives of trigonometric functions.

Possible Answers:

True

False

Correct answer:

True

Explanation:

This is true.  The chain rule is what allows us to differentiate composite functions.  Composite functions are functions that are within one another.  Take  for example.   in itself is a function, but so is .  We can let  and .  So the composite function would be, .

 

Now for the Chain Rule we multiply the derivative of the inside function by the coefficient of the outside function while differentiating the outside function as well.  will be the composite function .  The formula for the Chain Rule is:

 

.


Going back to our example of , we know that the derivative of  is  and the derivative of  is .  So the derivative of our composite function is .  Thus, every time we are differentiating trigonometric functions we are utilizing the Chain Rule whether we realize it or not.

Example Question #6 : Use Derivatives Of Trig Functions

What is the derivative of ?

Possible Answers:

Correct answer:

Explanation:

We must take the derivative of both the quantity of the tangent function and tangent itself to solve for this derivative.  Recall that the derivative of 

 

 

Example Question #7 : Use Derivatives Of Trig Functions

What is the derivative of  at ?

Possible Answers:

This derivative is undefined at this point

Correct answer:

This derivative is undefined at this point

Explanation:

We must start this problem by finding the derivative.  Recall that the derivative of the cosecant function is 

 

 

Now we must find the derivative of .  So we will plug  in for .

 

 

And so at the point of the graph of the derivative, the function is undefined.

 

 

Example Question #1 : Use Derivatives Of Trig Functions

True or False: When the derivative of  is negative but increasing, then the function  is increasing.

Possible Answers:

False

True

Correct answer:

False

Explanation:

Even though we are working with trigonometric functions, the rules of derivatives remain the same.  Since the graph of a derivative function is the graph of the rate of change of the original function, then when the graph of the derivative function is negative, the original function is decreasing.  Even when the derivative is increasing, if it is negative the original function is still decreasing, just by less of a factor.  When the derivative function is at zero, then the original function is constant.  When the derivative function is positive, then the original function is increasing.

Example Question #9 : Use Derivatives Of Trig Functions

Find the derivative of .

Possible Answers:

Correct answer:

Explanation:

We need to use the Chain Rule to take both the derivative of the trigonometric function and the quantity within the trig function.

 

 

 

Example Question #10 : Use Derivatives Of Trig Functions

What is the derivative of ?

Possible Answers:

Correct answer:

Explanation:

Recall that the derivative of the tangent function is .  So we need to take the derivative of the exponent of  and we also need the derivative of the actual tangent function.

 

 

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