Question

若(x+1/x)的平方等于9,则(x-1/x)的值等于

Answer 1

(x+1/x)^2=9

x^2+2*x*1/x+(1/x)^2=9

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

x^2+1/x^2=7

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

(x-1/x)^2=5

x-1/x=√5