若2x=-y,则x²-y²分之xy等于?
问题描述：
若2x=-y,则x²-y²分之xy等于?
答
2x=-y,y=-2x
x²-y²分之xy
xy/(x²-y²)=x*(-2x)/[x²-(-2x)^2]
=-2x²/(x²-4x²)
=-2x²/(-3x²)
=2/3