x^2+1/x^2-2=1/x^2 * [x^4-2x^2+1]=1/x^2 * (x^2-1)^2
因此:
sqrt(x^2+1/x^2-2)= sqrt(1/x^2 * (x^2-1)^2)
= 1/|x| * |x^2-1|
= -1/x * (1-x^2)
= (x^2-1)/x