1.解:(1)原式=-3x.
(2)原式=ab.
(3)原式=(2x²-x²)+(x-x)=x².
(4)原式=(3x²-2x²)+(4x-6x)+(-6+5)=x²-2x-1.
2.解:(1)原式=(2x²+x²)+ (-3x+4x) -2=3x²+x-2.当x=-1/2时,原式=3×(-1/2)² -1/2-2=-7/4.
(2)原式=(7a²+a²)+(-2ab+3ab)+(b²-2b²)=8a²+ab-b². 当a=-2,b=2时,原式= 8×(-2)^2+(-2)×2-2²=24.
3.解:(1)按x的降幂排列为-2x³-4x²+13x-6;按x的升幂排列为-6+13x-4x²-2x³.
(2)按x的降幂排列为-3x³+3x²y-3xy²+y³; 按x的升幂排列为y³-3xy²+3x²y-x³.
4.解:(1)原式=3a-b+5a-3b+3=(3a+5a)+(-b-3b)+3=8a-4b+3.
(2)原式=2b-3a-2a+3b-1=(-3a-2a)+(2b+3b)-1=-5a+5b-1.
(3)原式=4x²+2x²-2y²-3x²-3y²=(4x²+2x²-3x²)+(-2y²-3y²)=3x²-5y².
5.(1)a²-b² (2)a²-2ab+b² (3)a²-b²
6.解:原式=am-bm-(-bn+an)=(a-b)m-(a-b)n.
7.解:(1)原式=3a+2b+8c+2a-3b-5c=(3a+2a)+(2b-3b)+(8c-5c) = 5a –b +3c.
(2)原式=2xy+x²-y²-x²+y²+3xy=(x²-x²)+(-y²+y²)+(2xy+3xy)= 5xy.
(3)原式=3x²-(5x+4x-5-9x²)=3x²-5x-4x+5+9x²=(3x²+9x²)+(-5x-4x)+5 = 12x²-9x+5.