计算(3x+y-2)(4x-y+2)
问题描述：
计算(3x+y-2)(4x-y+2)
答
12*x^2+x*y-2*x-y^2+4*y-4
答
=12x^2-3xy+6x+4xy-y^2+2y-8x+2y-4
=12x^2-y^2+xy-2x+4y-4