# Homework Help: Derivative question help!

1. Oct 21, 2012

### Kolby

1. The problem statement, all variables and given/known data

Consider the following function of variable r, for r greater or equal to 0.
y(r)=(r^2-8r)exp(-r)

1. Find the value of the first derivative at r=8.00
2. Find the value of the second derivative at r=8.00
3. Find the value of r where y takes its meinimum value in the r is greater or equal to 0 interval
4. Find the value of r where y takes its maximum value in the r is greater or equal to 0 interval

Please explain how you do it too! I am so lost :(

2. Relevant equations

3. The attempt at a solution

2. Oct 21, 2012

### SHISHKABOB

looks like you need to take the derivative of the function y(r) and then plug in the values

3. Oct 21, 2012

### Kolby

I know but I have no idea how to do that, im new to physics so this is all new to me.

4. Oct 21, 2012

### voko

This has nothing to do with physics and everything to do with calculus. Have you studied it and have you studied derivatives in particular?

5. Oct 21, 2012

### Kolby

I have not learned anything about derivatives. My Physics Professor just decides to assign us 3 derivative problems over the weekend on MasteringPhysics :(

6. Oct 21, 2012

### voko

I am not sure what this could possibly mean. If you have not taken any calculus, then you won't be able to solve this problem.

7. Oct 21, 2012

### jamesnb

Is calculus a prerequisite for the physics course? Are you taking algebra based physics or calculus based physics?

8. Oct 21, 2012

### Staff: Mentor

The OP has not shown any effort. I am locking this thread.