(√ (1+X)-√ (1-X))/(√(1+X) +√ (1-X))=(√(1+x)-√(1-x)^2/2x=[2-2√(1-x^2)]/2x=[1+√(1-x^2)]/x求导{[1-√(1-x^2]/x}'=[x^2/√(1-x^2)-1+√(1-x^2)]/x^2=1/√(1-x^2)-1/x^2+√(1-x^2)/x^2 =1/√(1-x^2)+[√(1-x^2)-1]/x^2
