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

问题描述:

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

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