I am given $x=u+v$, $y=3u^2$, and $z=u-v$. I need to find the equation of the tangent plane at $(2,3,0)$. I understand that the equation of the tangent plane is $z=f_x(x_0,y_0)(x-x_0)+f_y(x_0,y_0)(y-y_0)$, since $z_0=0$. I have determined that $u=1$ and $v=1$ at $(2,3,0)$.
I'm confused as to how I determine $f_x$ and $f_y$ since my coordinates are in terms of $u$ and $v$.