Calculus AB : Calculate Higher Order Derivatives

Study concepts, example questions & explanations for Calculus AB

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Example Questions

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Example Question #41 : Differentiating Functions

On a closed interval, the function  is decreasing. What can we say about  and  on these intervals?

Possible Answers:

 is negative

 is negative

 is decreasing

Two or more of the other answers are correct.

 is decreasing

Correct answer:

 is negative

Explanation:

If  is decreasing, then its derivative is negative. The derivative of  is , so this is telling us that  is negative.

 

For  to be decreasing,  would have to be negative, which we don't know.

 

 being negative has nothing to do with its slope. 

 

For  to be decreasing, its derivative  would need to be negative, or, alternatively  would have to be concave down, which we don't know.

 

Thus, the only correct answer is that  is negative.

Example Question #41 : Differentiating Functions

On what intervals is the function  both concave up and decreasing?

Possible Answers:

Correct answer:

Explanation:

The question is asking when the derivative is negative and the second derivative is positive. First, taking the derivative, we get

Solving for the zero's, we see  hits zero at  and . Constructing an interval test,

 we want to know the sign's in each of these intervals. Thus, we pick a value in each of the intervals and plug it into the derivative to see if it's negative or positive. We've chosen  and  to be our three values.

Thus, we can see that the derivative is only negative on the interval .

 

Repeating the process for the second derivative,

The reader can verify that this equation hits  at . Thus, the intervals to test for the second derivative are 

.  Plugging in  and , we can see that the first interval is negative and the second is positive.

Because we want the interval where the second derivative is positive and the first derivative is negative, we need to take the intersection or overlap of the two intervals we got:

If this step is confusing, try drawing it out on a number line -- the first interval is from  to , the second from  to infinity. They only overlap on the smaller interval of  to .

 

Thus, our final answer is 

Example Question #43 : Differentiating Functions

If

and  ,

then find .

Possible Answers:

Correct answer:

Explanation:

We see the answer is  when we use the product rule.

 

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