Question

若x²+xy-2y²=0,则x²+3xy+y²/x²+y²

Answer 1

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

x=y或x=-2y

当x=y时：原式=(1+3+1)/(1+1)=2

当x=-2y时：原式=(4-6+1)/(4+1)=-1/5