F.2 maths question

運用公式 (a-b)^2=a^2-2ab+b^2

{ x - (1/x) } ^2
=x^2-2(x)(1/x)+(1/x)^2
=x^2-2+(1/x)^2
=3-2
=1

Expand [ x - (1/x) ] ^2
= x^2 - 2(x)(1/x) + (1/x)^2
= x^2 - 2 + 1/(x^2)
= [ x^2 + 1/(x^2)] - 2
= 3 - 2 --> since x^2 + 1/(x^2) = 3
=1

hope this helps =)