Question

已知x的平方-3x+1=0,求（x-1/x）的平方=?

Answer 1

x^2-3x+1=0

x^2+1=3x 两边除x

x+1/x=3 平方

x^2+2+1/x^2=9

x^2+1/x^2=7

x^2-2+1/x^2=5

(x-1/x)^2=5