Question

已知a等于2次方加xy加3y2次方,b等于x2次方减xy加2y2次方,求a减3b

Answer 1

a-3b=(x^2+xy+3y^2)-3(x^2-xy+2y^2)

=x^2+xy+3y^2-3x^2+3xy-6y^2

=-2x^2+4xy-3y^2