Second Derivative in Terms of Y

[whoopie88]

Homework Statement

Find the second derivative of 4x^2 + 3x - 9y^2. Answer in terms of y.

Homework Equations

All derivative formulas.

The Attempt at a Solution

[PLAIN]http://http://i52.tinypic.com/2w2ptex.jpg

I can't get much further than this; the thing that gets me is how to put everything in terms of y. Help? Thanks!

 

[HallsofIvy]

You can't. The problem you give makes no sense. If you have an equation like $4x^2+ 3x- 9y^2= 0$ then y is defined as an "implicit" function of x and you can find the first and second derivatives of y with respect to x.

Or, if you have a function $f(x,y)= 4x^2+ 3x- 9y^2$ you can find the the second derivative of f with respect to y.

Please check and tell us what the problem really is.