u=sinx
∂u/∂x = cosx
v=y^2
∂v/∂y= 2y
z=e^(u-2v)
∂z/∂x = e^(u-2v) .∂u/∂x
= cosx.e^(u-2v)
∂z/∂y= e^(u-2v) .(-2(∂v/∂y))
=-4y.e^(u-2v)