1.x^2-4x+4=(x-2)^2
9x^2-3xy+1/4y^2=(3x-1/2y)^2
两个
2.我猜应该是(2x+y)^2+(2x-y)^2
答案是8x^2+2y^2
3.=(m)^2-(2n-1)^2
4.21分之517
5.原式=(-4x)^2+2*(-4x)*(3y)+(3y)^2
=16x^2-24xy+9y^2
6.原式=-(x+2y)(x+2y)
=-(x+2y)^2
=-[(x)^2+2*x*2y+(2y)^2]
=-x^2-4xy-4y^2
7.原式=(2x-3y)^2+(3x-4y)(3x+4y)
=4x^2-12xy+9y^2+9x^2-16y^2
=13x^2-12xy-7y^2
8.原式=x(x^2+2x+1)-x^3-x^2-x-7
=x^3+2x^2+x-x^3-x^2-x-7
=x^2-7
∵x^2-4=0
∴x^2=4
∴x^2-7=4-7=-3
9.N=-3ab
10.=3^2+(-1)^2=10
11.减少了a^2-(a-b)^2
=a^2-(a^2-2ab+b^2)
=2ab-b^2
12.xy=1
13.7
14.13
15.原式=(100-0.2)^2
=100^2-2*100*0.2+(0.2)^2
=9960.04
16.原式=[(2a+b)(2a-b)]^2
=(4a^2-b^2)^2
=16a^2-8a^2b^2+b^4
17.原式=[a-(2b-c)][a+(2b-c)]
=a^2-(2b-c)^2
=a^2-(4b^2-4ab+c^2)
=a^2+4ab-4b^2-c^2
18.∵a-b=3
∴(a-b)^2=9
∴a^2-2ab+b^2=9
∴原式=9分之2
19.∵(x+y)^2=25,(x-y)^2=9
∴x^2+2xy+y^2=25——(1)
x^2-2xy+y^2=9——(2)
∴(1)+(2)得：
2(x^2+y^2)=34
∴x^2+y^2=17
∴2xy=8
∴xy=4
20.符合
理由：工业园面积为：(a+b)^2m^2
即(a^2+2ab+b^2)m^2
而砖瓦窑与矩形土坑面积之和为：
(a^2+b^2+2ab)m^2
所以符合要求
21.=1-4a^2
22.=-6
23.=2010
24.原式=a^2-b^2+b^2-2ab
=a^2-2ab
当a=2,b=1时,
原式=a^2-2ab
=2^2-2*2*1
=4-4=0
25.展开代数式有：
x^4+(3+n)x^3+(3n-m-3)x^2-(mn+9)x+3m
∵不含x^3、x^2项
∴3+n=0,3n-m-3=0
解得：n=-3,m=-12.
希望能及时采纳.
