5、(2008浙江金华)化简a+b+(a-b)的最后结果是(　 )C

A、2a+2b　 B、2b　 C、2a　 D、0

4、(2008浙江金华)如果+3吨表示运入仓库的大米吨数，那么运出5吨大米表示为(　 )A

A、－5吨　 B、+5吨　 C、－3吨　 D、+3吨　

3、(2008湖南邵阳)等于(　　 )D

A．　　　　　 B．　　　　 C．　　　　　 D．

2．(08山东日照)下列计算结果正确的是(　　 )　 C　

A．　 B．= 　　

C．　　 D．

1.(2008年四川省宜宾市)下列各式中，计算错误的是(　 )

A. 2a+3a=5a　　　　　　　　 B. –x²·x= -x³　　　　　　　　　　 C. 2x-3x= -1　　　　　　　　 D.(-x³)²= x⁶

答案：C

76. 解：　 　………………………………………2分

＝　　　　 …………………………………………………………3分

＝　　　　 …………………………………………………………4分

＝．　　　　 ……………………………………………………………………5分

当时，原式＝．　 …

75. 解：去分母，得

．·············································································· (3分)

整理，得．····················································································· (2分)

，．····························································································· (4分)

经检验，是增根，是原方程的根．··················································· (1分)

所以，原方程的根是．

74. 解：原式＝　　 ……………………………2分

＝　　　　 …………………………………………3分

＝．　　　 ……………………………………………………………4分

当，时，

原式＝．　

73. 解：方程两边都乘以，得：

　　　　　　　　　　　　 解得：

　 　　　　　　　　　　　　 经检验：是原方程的根；

72. ．解：设原计划每小时抢修的路线长为，根据题意，得

································································································ 5分

解之得

························································································································ 7分

检验：是原方程的解，且符合题的实际意义．

答：原计划每小时抢修的路线长为400m．···································································· 8分