已知x/y=3,求分式(x^+2xy-3y^2)/(x^2-xy+y^2)的值

Question

已知x/y=3,求分式(x^+2xy-3y^2)/(x^2-xy+y^2)的值

Answer 1

由x/y=3
得x＝3y
(x^2+2xy-3y^2)/(x^2-xy+y^2)
=(9y^2+6y^2-3y^2)/(9y^2-3y^2+y^2)
=12y^2/7Y^2
=12/7