1.3ab-4ab+8ab-7ab+ab a=1,b=2 2.2y+(-2y+5)-(3y+2) x=3,y=4.5 3.已知A=x3-2x2+x-4,B=2x3-5x+3,计算A+B 4.5(x-2y)2-3(-x+2y)-100 ,2y-x=5 5.9a2+[7a2-2a-(-a2+3a)]= a=6
