2018-2019学年湘教版七年级上《2.3代数式的值》同步练习含答案

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1、2.3代数式的值一、选择题1.当x=1时，代数式ax3﹣3ax+4的值是7，则当x=﹣1时，这个代数式的值是（　　）A. 7                                           B. 3                                           C. 1                                           D. -7【答案】C2.已知x2﹣2x﹣5=0，则2x2﹣4x的值为（　　）A. -10                    

2、              B. 10                                  C. ﹣2或10                                  D. 2或﹣10【答案】B3.已知a﹣b=﹣3，c+d=2，则（b+c）﹣（a﹣d）的值为（  ）A. 1                                         B. 5                                         C. ﹣5                        

3、                 D. ﹣1【答案】B4.已知：当x=2时，多项式x4﹣bx2+c的值为2016，当x=﹣2时，多项式x4﹣bx2+c的值为（　　）A. -2016                                  B. -2015                                  C. 2016                                  D. 2015【答案】C5.如果a与b互为相反数，x与y互为倒数，则代数式

4、a+b

5、﹣2xy值为（ ）A. 0 

6、                                    B. ﹣2                                     C. ﹣1                                     D. 无法确定【答案】B6.二次三项式3x2﹣4x+6的值为9，则的值为（　　）A. 18                                          B. 12                                          C. 9     

7、                                     D. 7【答案】D7.

8、a

9、=1，

10、b

11、=2，

12、c

13、=3，且a>b>c，则a+b-c=(     ）．A. -2                                        B. 0                                        C. -2或0                                        D. 4【答案】C8.已知：a＋b＝m，ab＝－4,化简（a－2）（b－2）的

14、结果是A. －2m                                    B. 2m                                    C. 2m－8                                    D. 6【答案】A9.若

15、a

16、=7，b的相反数是2，则a+b的值（）A. －9                              B. －9或＋9                              C. ＋5或－5                   

17、           D. ＋5或－9【答案】D10.如果四个互不相同的正整数m，n，p，q满足(6-m)(6-n)(6-p)(6-q)=4，那么m+n+p+q=(  )A. 24                                         B. 25                                         C. 26                                         D. 28【答案】A11.已知代数式x+2y的值是5，则代数式2x+4y+1的值

18、是（　　）A. 6                                          B. 7                                          C. 11                                          D. 12【答案】C12.已知