Question

若x^2+xy-2y^2=0,则x^2+3xy+y^2/x^2+y^2=?

Answer 1

(x+2y)(x-y)=0

x=-2y或x=y

x=-2y

原式=(4y²-6y²+y²)/(4y²+y²)

=-y²/5y²

=-1/5

x=y

原式=(y²+3y²+y²)/(y²+y²)

=5y²/2y²

=5/2

所以原式=-1/5或5/2