# Implicit Differentiation

1. Feb 20, 2008

### hard_assteel

[SOLVED] Implicit Differentiation

-4x^2+3xy+4y^3=-328

This is at the point (3,-4)
and i am trying to find m

2. Relevant equations

3. The attempt at a solution

here is my work

-4x^2+3xy+4y^3=-328
-8x+3xy'+3y+12y^2y'=0
-8x+3y=-3xy'-12y^2y'
-8x+3y=[-3x-12y^2]y'
y'=(-8x+3y)/(-3x-12y^2)
plug in x=1,y=3 then solve and get
m=-12/67
can you find the error?
It would be very much appreciated
thank you.

Last edited: Feb 20, 2008
2. Feb 20, 2008

### nicksauce

Try plugging in the values to your final expression again.

3. Feb 20, 2008

### hard_assteel

0h, the answer is correct, it just needs to be not negative, thank you. i was about to go crazy

Last edited: Feb 20, 2008
4. Feb 20, 2008

### cristo

Staff Emeritus
I don't agree that your numerical answer is correct, regardless of the sign.

5. Feb 20, 2008

### hard_assteel

yeah, its correct i just checked. thankx for helping me

6. Feb 21, 2008

### cristo

Staff Emeritus
Well, maybe it is now you've changed the point to (3,-4)!