Hello.
I have a real issue with fractions, it seems! can anyone help me understand how to find the 2nd order derivitives for
z=xy/(x+y)
thanks for any help
There are four to find. $\displaystyle \frac{\partial ^2z}{\partial x^2}$, $\displaystyle \frac{\partial ^2z}{\partial y^2}$, $\displaystyle \frac{\partial ^2z}{\partial xy}$ and $\displaystyle \frac{\partial ^2z}{\partial yx}$
You need to find $\displaystyle \frac{\partial z}{\partial x}$ and $\displaystyle \frac{\partial z}{\partial y}$ first, use the quotient rule.