# Math Help - implicit differentiation

1. ## implicit differentiation

Find $\frac{d^2y}{dx^2}$ by implicit differentiation: $2x^3-3y^2=8$

So far I get
$\frac{dy}{dx}=\frac{x^2}{y}$
$\frac{d^2y}{dx^2}=\frac{2y}{x}$ <----- incorrect

correct answer= $\frac{2xy^2-x^4}{y^3}$

How do i find the correct answer?

2. Originally Posted by yoman360
Find $\frac{d^2y}{dx^2}$ by implicit differentiation: $2x^3-3y^2=8$
show some effort ...

what did you get for $\frac{dy}{dx}$ ?

3. I get $\frac{dy}{dx}=\frac{x^2}{y}$

i keep getting the same answer

this one is difficult

4. $2x^3-3y^2=8$

$6x^2 - 6y \cdot y' = 0$

$y' = \frac{x^2}{y}$

$y'' = \frac{2xy - x^2y'}{y^2}$

$y'' = \frac{2xy - \frac{x^4}{y}}{y^2}$

$y'' = \frac{2xy^2 - x^4}{y^3}
$

5. Originally Posted by skeeter
$2x^3-3y^2=8$

$6x^2 - 6y \cdot y' = 0$

$y' = \frac{x^2}{y}$

$y'' = \frac{2xy - x^2y'}{y^2}$

$y'' = \frac{2xy - \frac{x^4}{y}}{y^2}$

$y'' = \frac{2xy^2 - x^4}{y^3}
$
oh i see now I forgot to use the quotient rule