y=1/(1+√x)-1/(1-√x) =(1-√x) /【(1+√x)(1-√x)】- (1+√x)/【(1+√x)(1-√x)】 =【(1-√x) - (1+√x)】/(1-x) =2√x / (x-1)∴y′=2×{0.5【x^(-0.5)】(x-1)— √x }/(x-1)² ={【x^(-0.5)】(x-1)— 2√x }/(x-1)² =【(x-1)— 2x 】/【√x (x-1)²】 =-(x+1)/【√x (x-1)²】