Differentiating a constraint equation

[w3390]

Homework Statement

z = cr^2

Homework Equations

The Attempt at a Solution

I have a pretty simple question. What is the second derivative of the z equation.

I know that z' = 2crr'.

Am I correct to say that z'' = 2cr'^2 or is it something else?

Hopefully my question makes sense.

 

[fzero]

There's a 2nd term involving r''. Use the product rule (fg)' = f' g + f g'.

 

[w3390]

Okay, thank you. That is what I was looking for. I just wasn't sure if I had to treat my r' as another variable or if I could consider it to be constant with the 2c. Thanks very much.