如果x-2y=7,xy=3,则2xy-4x+2x+5=

问题描述:

如果x-2y=7,xy=3,则2xy-4x+2x+5=

2xy-4y+2x+5
=2xy+2(x-2y)+5
=2*3+2*7+5
=6+14+5
=25
-4y吧?