Originally Posted by

**bobred** Hi

Not sure if this is in the right section, if not could someone suggest a better one?

I am given the function below and told that $\displaystyle x=3$ and $\displaystyle y=-5$ with a tolerance of $\displaystyle \pm0.02$ and $\displaystyle \pm0.03$ respectively.

$\displaystyle f(x,y)=x^{3}+x^{2}y+y^{2}+2y$

I am asked to find the accuracy of $\displaystyle f(x,y)$, I have

$\displaystyle \frac{\partial f}{\partial x}=3x^{2}+2xy$ and $\displaystyle \frac{\partial f}{\partial y}=x^{2}+2y+2$ using the formula $\displaystyle \delta f=\frac{\partial f}{\partial x}\delta x + \frac{\partial f}{\partial y}\delta y$, my question is what value do I use for $\displaystyle \delta x, \delta y$, do I use 0.02 and 0.03 or do I use 0.04 and 0.06?

Thanks James