2、(1)a²-11a+7
(2)4t+5
(3)x³+2x²+2x+1
(4)2x³+x²-x+3
3、解:(1)(1/3x—y)²+(1/3x+y)²
=1/9x²--2/3xy+y²+1/9x²+2/3xy+y²
=2/9x²+2y²;
(2)(x+2y-1/2)(x-2y+1/2)
=[x+(2y-1/2)][x-(2y-1/2)]
=x²- (2y-1/2) ²
=x²- (4y²-2y+1/4)
=x²-4y²+2y-1/4
4、(1)-2x
(2)2x²y³
(3)2y-8x
(4)y-2x
5、解:(1) 2x(x²-x+1) -x(2x² +2x-3)
=2x³-2x²+2x-2x³-2x²+3x
=- 4x2 +5x.
当x=-1/2时,
-4x²+5x
=-4×(-1/2)²+5×(-1/2)
=-4×1/4-2/5
=-7/2
(2)(2x-1/2y)(2x+1/2y)-(2x-1/2y)²
=(2x)²-(1/2y)²-(4x²-2xy+1/4y²)
=4x²-1/4y²-4x²+2xy-1/4y²
=-1/2y²+2xy
当x=1/4,y=-1时,-1/2y²+2xy
=-1/2×(-1)²+2×1/4×(-1)
=-1/2×1-1/2
=-1
6、解:(1)3x(x+2)+(x+1)(x-1)
=4(x²+8),
3x²+6x+x²-1=4x²+32,
6x=33,
x=11/2
由①得xy-5x-xy+2y=12,即-5x+2y=12.③
由②得12xy- 2x+ 8y-8xy= 4xy+12,即-2x+8y=12.④
③×4,得-20x+8y=48.⑤
由④-⑤,得18x=- 36,所以x=-2.
把x=-2代入③,得-5×(-2)+2y=12,所以y=1.
所以原方程组的解
7、解:(3x+4)(3x-4)>9 (x-2)(x+3),
9x²-16>9(x²+x-6),
x<38/9.
所以不等式的正整数解为1,2,3,4.
9、解:S= (2.5a+l.5a) (a+2a+2a+2a+a)- (2a×2.5a×2) 32a²-10a²=22a² (cm²).
当a=10cm时,S=22×10²=2200(cm²).
10、解:剩余空地的面积为ab-ac-bc+c².
11、(1)25c² 5c
(2)1/9n² 1/3n
12、(1)(x+3a) ²
(2)(x-a)(x-2a)
13、解:因为4x²+mx+36是一个完全平方式,
所以4x²+mx+36
= (2x) ²+mx+(±6) ²
=(2x±6)2,
所以m=±24.