Question

若x²-4y²=-15,2y-x=3,则x+2y=______.

Answer 1

∵x²-4y²

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

=-15

又∵2y-x=3

∴-(x-2y)=3,x-2y=-3

∴x+2y=-15/(x-2y)=(-15)/(-3)=5