设z=㏑√(x²+y²)求（dz/dx）²+(dy/dx)²
问题描述：
设z=㏑√(x²+y²)求（dz/dx）²+(dy/dx)²
答
z=0.5㏑(x²+y²)
dz/dx =x/(x²+y²)
dy/dx=y/(x²+y²)
所以（dz/dx）²+(dy/dx)²=1/(x²+y²)