3A+B=3(4x²-4xy+y²)+(x²+xy-5y²)=12x²-12xy+3y²+x²+xy-5y²=13x²-11xy-2y²
3A+B=3(4x²-4xy+y²)+(x²+xy-5y²)=12x²-12xy+3y²+x²+xy-5y²=13x²-11xy-2y²=（x-y）（13x+2y)
