z = yln[x+√(x²+y²)]+3x-2y
∂z/∂x = {y/[x+√(x²+y²)]}{1 + x/√(x²+y²)} + 3
= y[√(x²+y²)+x]/[x+√(x²+y²)][√(x²+y²)] + 3
= y/[√(x²+y²)] + 3