1.(1)1800a (2)a(10-a)cm².
2.解:(1)(4a+4)cm. (2)a(10-a)cm².
3.解:如下表所示.
4.提示:2/5 m.
5.提示:200+x.
6.提示:p(1-10%)²元.
7.解:如图12所示.
8.解:(1)-4x²y²的次数是4,系数是-4;2ab/3的次数是2,系数是2/3;2a的次数是1,系数是2;-ab²的次数是3,系数是-1.
(2)a²+2a-1的项数是3,次数是2;t-1的项数是2,次数是1;x²-2xy-y²+1的项数是4,次数是2.
9.(1)-a²+ab+b²+1
(2)3x²y,-x²y
(3)x²-2x+1
(4)x-y
(5)b-cb-c
10.解:(1)3(a²-2ab)-(-ab+b²)=(3a²-6ab)-(-ab+b²)=3a²-6ab+ab-b²=3a²-5ab-b².
(2)-2(2x²-x+4)+3(x²-2x+3)=-(4x²-2x+8)+(3x²-6x+9)=-4x²+2x-8+3x²-6x+9=-x²-4x+1.
11.解:(1)(3x²-2)-(4x²-2x-3)+(2x²-1)=3x²-2-4x²+2x+3+2x²-1=(3x²-4x²+ 2x²)+2x+(-2+3-1)=x²+2x.当x=-2时,原式=(-2)²+2×(-2)=4+(-4)=0.
(2)3x²y-[2x²y-(2xyz-x²z)-4x²z]-xyz=3x²y-2x²y+2xyz-x²z+4x²z-xyz=(3x²y -2x²y))+(2xyz-xyz)+(-x²z+4x²z)=x²y+xyz+3x²z.当x=-2,y=-3,z=1时,原式=(-2)²×(-3)+(-2)×(-3)×1+3×(-2)²×1=6
12.解:由题意可知第2排有(a+2)个座位,第3排有(a+4)个座位,第4排有(a+6)个座位,则第n排的座位数m可表示为m=a+2(n-1).当a=20,n=12时,m=20+2×(12-1)=20+22=42.