Question

已知x+x负1次方=5,求x+x负3次方的值

Answer 1

x+(1/x)=5

x^3+(1/x^3)

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

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

=5*(5^2-3)

=110