已知A=4x²-4xy+y²,B=x²+xy-5y²,求：⑴A-3B;⑵2A+B帮个忙哩

已知A=4x²-4xy+y²,B=x²+xy-5y²,求：⑴A-3B;⑵2A+B帮个忙哩
已知A=4x²-4xy+y²,B=x²+xy-5y²,求：⑴A-3B;⑵2A+B
帮个忙哩

已知A=4x²-4xy+y²,B=x²+xy-5y²,求：⑴A-3B;⑵2A+B帮个忙哩
已知A=4x²-4xy+y²,B=x²+xy-5y²
则,A-3B
=4x^2-4xy+y^2-3(x^2+xy-5y^2)
=4x^2-4xy+y^2-3x^2-3xy+15y^2
=x^2-7xy+16y^2
2A+B
=2(4x^2-4xy+y^2)+x^2+xy-5y^2
=8x^2-8xy+2y^2+x^2+xy-5Y^2
=9x^2-7xy-3y^2