Question

已知x/y =2,求(x^2-xy+3y^2)/(x^2+xy+6y^2) 的值．

Answer 1

x/y =2,--->x=2y

(x^2-xy+3y^2)/(x^2+xy+6y^2)

=(4y^2-2y^2+3y^2)/(4y^2+2y^2+6y^2)

=5/12