Question

已知：x²-y²=4xy,求(x的四次方+y的四次方）除以（xy）²

Answer 1

x^4+y^4=(x^2-y^2)^2+2x^2y^2

(x^4+y^4)/(x^2y^2)=((x^2-y^2)^2+2x^2y^2)/(x^2y^2)

=((4xy)^2+2x^2y^2)/(x^2y^2)

=(16x^2y^2+2x^2y^2)/(x^2y^2)

=18