已知:A=2x²+3xy-2x-1,B=-x²+xy-1

问题描述:

已知:A=2x²+3xy-2x-1,B=-x²+xy-1
(1)求3A+6B的值
(2)若3A+6B的值与x的无关,求y的值

(1)
3A+6B
=3(2x²+3xy-2x-1)+6(-x²+xy-1)
=6x²+9xy-6x-3-6x²+6xy-6
=6x²-6x²+9xy+6xy-6x-3-6
=15xy-6x-9
(2)
3A+6B
=15xy-6x-9
=(15y-6)x-9
若3A+6B的值与x的无关,则
15y-6=0
15y=6
y=6/15=2/5