Question

已知A=2x的2次方-3xy+y的2次方,B=x的2次方+2xy-3y的2次方,求A+B;A-2B

Answer 1

A+B=2x^2-3xy+y^2+x^2+2xy-3y^2
=3x^2-xy-2y^2
=(3x+2y)(x-y)
A-2B=2x^2-3xy+y^2-2(x^2+2xy-3y^2)
=2x^2-3xy+y^2-2x^2-4xy+6y^2
=-7xy+7y^2
=7y(y-x)