Originally Posted by

**gocubsgo708** Well I know that to take a derivative by the definition, the formula is:

f(x+h) - f(x)/h

and to take the derivative of a multivariable function with respect to x by the definition is:

f(x+h,y) - f(x)/h

I don't know why, but the y in there seems to confuse me.

Was wondering if anyone could show me how to take the derivative of the following functions with respect to x. Make sure to do it by the definition.

f(x,y) = x^2 + 2y^2

f(x,y) = 2x+3y+5

Thanks for your help! I'm brand new here.