amaths dy/dx

Find the derivative

圖片參考：http://g.imagehost.org/0372/ScreenHunter_01_Mar_22_01_27.gif

y = [x - (x^2 - 1)^0.5]^0.5
d/dx = {0.5 [x- (x^2 - 1)^0.5]^(-0.5)} [ 1- 0.5 (2x) (x^2 - 1)^(-0.5)]
= [1 - x/(x^2 - 1)^0.5 ] / {2 [x - (x^2 - 1)^0.5]^0.5}