Z ＝ln√(xy)∂Z/∂x = [1/√(xy)][0.5y/√(xy)] = 1/2x∂Z/∂y = [1/√(xy)][0.5x/√(xy)] = 1/2y∂²Z/∂x∂y = 0∂²Z/∂x² = -1/2x²∂²Z/∂y² = -1/2y²
