已知A=3x2+3y2-5xy,B=2xy-3y2+4x,求①2A-B已知A=3x²+3y²-5xy,B=2xy-3y²+4x,求①2A-B②A-2B③3A-4B
问题描述：
已知A=3x2+3y2-5xy,B=2xy-3y2+4x,求①2A-B
已知A=3x²+3y²-5xy,B=2xy-3y²+4x,求①2A-B②A-2B③3A-4B
答
①2A-B
=2(3x2+3y2-5xy)-(2xy-3y2+4x)
=6x²+6y²-10xy-2xy+3y²-4x
=6x²+9y²-12xy-4x
②A-2B
=(3x2+3y2-5xy)-2(2xy-3y2+4x)
=3x²+3y²-5xy-4xy+6y²-8x
=3x²+9y²-9xy-8x
③3A-4B
=3(3x2+3y2-5xy)-4(2xy-3y2+4x)
=9x²+9y²-15xy-8xy+12y²-16x
=9x²+21y²-23xy-16x