#### Arden1528

I understand the formula to find this. You have to find the partial derv. of x and y then plug in (3,4) to get a value. Then take the partial derv. of x and multiply it by a, and partial derv. of y multiplied by b.

fx(3,4)a+fy(3,4)b

fx=partial derv of x

fy = partial derv. of y

the answer in the back of the book is 23/10, I get 23/3. So it must be in my partials? any help is very much apperciated.