Please help me in these 2 problems:
1. f(x,y)= x^2 / y, need fx and fy!
2.f(x,y)= x sin(xy), need fx and fy!
my point is, the constant stays! if you have a constant multiplying a variable, then the constant does not disappear when you differentiate. it stays there and multiplies the variable. this is a rule of differentiation you should be familiar with. $\displaystyle \frac d{dx} [cf(x)] = c \frac d{dx}f(x)$