u=arctan[(x-y)⁸]
∂u/∂x=1/[1+(x-y)¹⁶]·8(x-y)⁷=8(x-y)⁷/[1+(x-y)¹⁶]
∂u/∂y=1/[1+(x-y)¹⁶]·-8(x-y)⁷=-8(x-y)⁷/[1+(x-y)¹⁶]
u=arctan⁸(x-y)
∂u/∂x=8arctan⁷(x-y)·1/[1+(x-y)²]=8arctan⁷(x-y)/[1+(x-y)²]
∂u/∂y=8arctan⁷(x-y)·-1/[1+(x-y)²]=-8arctan⁷(x-y)/[1+(x-y)²]
y=arctan[(x-y)⁸]是一元隐函数,求偏导数?