1. [SOLVED] find second derivative

hey, i need help with this problem :

Instructions: find d^2y/dx^2 in terms of x and y

x^2 + y^2 = 36

( i can find the first derivative (y' = -x/y) but i don't understand how to get the second derivative (answer is supposedly -36/y^3)

all help is appreciated!

2. $\displaystyle \frac{d}{dx}\left(\frac{-x}{y}\right) =$

$\displaystyle \frac{(y)(-1) - (-x)(y')}{y^2} =$

$\displaystyle \frac{-y + x \cdot \frac{-x}{y}}{y^2} =$

$\displaystyle \frac{y\left(-y + x \cdot \frac{-x}{y}\right)}{y \cdot y^2} =$

$\displaystyle \frac{-y^2 - x^2}{y^3} = -\frac{36}{y^3}$

3. Thanks!

Thank you so much!
I finally get it.