哦,刚才最后一步化简错了,更正一下：z'=1/[1+(x/y)²]* (x/y)'=1/[1+(x/y)²] *(y-xy')/y²=(y-xy')/(y²+x²)而y'=1/[2√(x²+1)]*2x=x/√(x²+1)所以z'=[√(x²+1)-x²/√(x&...