Question

已知x+1/x=3,求x^2+1/x^2和(x-1/x)^2的值

Answer 1

答：

x+1/x=3

x^2+1/x^2=(x+1/x)^2-2=3^2-2=9-2=7

(x-1/x)^2=x^2-2+1/x^2=7-2=5

所以：

x^2+1/x^2=7

(x-1/x)^2=5