已知x+y=4,xy=-2,求代数式3(xy+2y)-(xy-6x)

问题描述:

已知x+y=4,xy=-2,求代数式3(xy+2y)-(xy-6x)

3(xy+2y)-(xy-6x)
=3xy+6y-xy+6x
=2xy+6(x+y)
=2×(-2)+6×4
=-4+24
=20