1. ## Partial derivatives..

I'm looking for the indicated second-order partial derivative for the function f(x,y).

f(x,y)=(1+2xy^2)^8

What I have is:

fx=(2y^2)^8 fy=(4xy)^8

fxx=0 fyy=(4x)^8

fxy=(4y)^8 fyx=4^8

I'm not good at the language of math so I'm not sure if I need to go on and if so, if I have even done what I have right. Any help is more than appreciated.

2. Originally Posted by halborse
I'm looking for the indicated second-order partial derivative for the function f(x,y).

f(x,y)=(1+4xy^2)^8

What I have is:

fx=(2y^2)^8 fy=(4xy)^8

fxx=0 fyy=(4x)^8

fxy=(4y)^8 fyx=4^8

I'm not good at the language of math so I'm not sure if I need to go on and if so, if I have even done what I have right. Any help is more than appreciated.
When you take partial derivative w.r.t x, consider y as a constant.
So $\displaystyle f_x=8(1+4xy^2)^74y^2$
$\displaystyle f_y=(8(1+4xy^2)^78xy$
Can you continue from here?

3. ## Thanks

I made an error when I wrote it down. I have since corrected this, but thank you for your help thus far. I just needed to check my numbers against someone else and I think you helped enough for me to do so. thank you once again.

4. ## my math is weak

I still can't see how to make this work. and when I use my Ti-89 I just end up with y=0. Wish it would show me the steps. Maybe you can. Please?