a=2x^2+2xy-2x-1, b=x^2-xy+1, 3a-6b与x无关 ,求y
问题描述：
a=2x^2+2xy-2x-1, b=x^2-xy+1, 3a-6b与x无关 ,求y
答
3a-6b
=3(2x^2+2xy-2x-1)-6(x^2-xy+1)
=6x^2+6xy-6x-3-6x^2+6xy-6
=12xy-6x-9
=6x(2y-1)-9
由于3a-6b与x无关
则2y-1=0
y=1/2