1. D 2.B 3.C 4.C 5.B
6. b²c²-4a²
7.- 2a² +5b
8.a²+2ab+b²-1
9.x⁴-1
10.解:(1)原式=4x²-9y⁴
(2)原式=a⁴-16b⁴
(3)原式=(500 -3)( 500 +3)= 250000 -9= 249991.
11.解:
(1)原式=(4x²-y²)(2x—y)=8x³-4x²y-2xy²+y³.
(2)原式=a²-(2b -3c)²=a²-4b²+12bc-9c².
(3)原式=(100-1)(100+1)(10000+1)=(10000-1)(10000+1)=10⁸-1
12.解:原式=xy+y²+x²-y²-x²=xy,当x=-2,y=1/2时,原式=(-2)×(1/2)=-1
13.解:∵正方形面积为x² cm²,长方形面积为(x+2)(x-2)=(x²-4)(cm²).
∴正方形面积大,大4cm².
14.解:∵9x² - 16 =9x²+9x- 54,∴9x=38,∴x=38/9.
15.(2n-1)(2n+1) =(2n)²-1