22.已知x+4y=-1,xy=5,求(6xy+7y)+[8x-(5xy-y+6x)]的值.

问题描述:

22.已知x+4y=-1,xy=5,求(6xy+7y)+[8x-(5xy-y+6x)]的值.

原式=6xy+7y+8x-5xy+y-6x
=xy+8y+2x
=xy+2(x+4y)
=5-2
=3

原式=6xy+7y+8x-5xy+y-6x=xy+8y+2x=xy+2(x+4y)=5-2=3