1.2x^2,a+3
2.34
3.3
4.1
5.5
6.x=1/2,y=-1/2
7.7a-b
8.C
9.B
10.B
11.原式=-2xy(2x-y+6)
12.原式=[(2x-y)+(x-2y)][(2x-y)-(x-2y)]=(3x-3y)(x+y)
13.原式=(x+2y)(x-2y)-3(x-2y)=(x-2y)(x+2y-3)
14.∵x+y=8 ∴(x+y)^2=64 → x^2+2xy+y^2=64
(x-y)^2=4 → x^2-2xy+y^2=4
两式相加,得2(x^2+y^2)=68 ∴x^2+y^2=34
15.两边同乘a,得a^3+a^2-2a=3a → a^3=a-a^2
a^3+2a^2+1999=a-a^2+2a^2+1999=a+a^2+1999
∵a^2+a+2=3 ∴a^2+a=1
∴a+a^2+1999=1+1999=2000
16.根据方程组解得7y=4
∵x-3y=1 ∴3y-x=-1
7y（x-3y）^2-2(3y-x)^3=4×1^4-2×(-1)^3=6
17.图呢?