单元测试题（二）
八年级数学
（测试内容：第二章 勾股定理与平方根）
班别 座号 姓名 成绩 ．
说明：1．可以使用计算器，但未注明精确度的计算问题不得采取近似计算，建议根据题型特点把握好使用计算器的时机．
2．本试卷满分100分，在90分钟内完成．相信你一定会有出色的表现！
一、填空题：本大题共10小题；每小题3分，共30分．请将答案填写在题中的横线上．
1．在
△ABC中，∠C＝90°．若a＝5，b＝12，则c＝
．
2．如图，要从电线杆离地面8
的C处向地面拉一条长10的电缆，则地面电缆固定点A到电线杆底部B的距离是
．
3．等腰直角三角形直角边长为1，则斜边长为 ．
4．等边三角形边长为2，则面积为 ．
5．9的算术平方根是 ．
6．2x＋1的算术平方根是2，x＝ ．
7．2是________的立方根．
8．若a与b互为相反数，则它们的立方根的和是 ．
9．绝对值不大于3的所有整数是 ．
10．边长为7，24，25的△ABC内有一点P到三边距离相等，则这个距离为 ．
二、选择题：本大题共8小题；每小题3分，共24分．在每小题给出的四个选项中，只有一项是正确的，请将正确答案前的字母填入题后的括号内．每小题选对得3分，选错，不选或多选均得零分．
11．····························································································································································· 
的平方根是 （ ）．
（A）3 （B）±3 （C）9 （D）±9
12．····························································································································································· 下列说法正确的是 （ ）．
（A）－4的平方根是±2
（B）任何数的平方是非负数，因而任何数的平方根也是非负数
（C）任何一个非负数的平方根都不大于这个数
（D）2是4的平方根
13．····························································································································································· 一个数的平方根与立方根相等，则这个数是·············································································································································· （ ）．
（A）1 （B）±1 （C）0 （D）－1
14．如果－b是a的立方根，那么下列结论正确的是······················································ （ ）．
（A）－b也是－a的立方根 （B）b是a的立方根
（C）b是－a的立方根 （D）±b都是a的立方根
15．····························································································································································· 与数轴上的点一一对应的数是····························································································································································· （ ）．
（A）整数 （B）有理数 （C）无理数 （D）实数
16．····························································································································································· 一个数等于它的倒数的9倍，则这个数是··················································································································································· （ ）．
（A）3 （B）
（C）±3 （D）±
17．····························································································································································· 周长为24，斜边长为10的直角三角形面积为·············································································································································· （ ）．
（A）12 （B）16 （C）20 （D）24
18．····························································································································································· 等腰三角形ABC底边上的高AD＝
BC，AB＝
，则△ABC面积为··················································································· （ ）．
（A） （B）1 （C）2 （D）4
三、解答题：本大题共4小题，共46分．解答应写出文字说明或演算步骤．
19．（11分）如图，一个圆桶的底面半径为30cm，高为80cm，求桶内能容下的最长的木棒长．
20．（11分）
如图，在森林公园探宝游戏活动中，小东和伙伴们先向东走8千米，又向北走3千米，遇到障碍后又向西走3千米，再折向北5千米，然后再向东走1千米，终于找到宝藏．问出发点与宝藏点的直线距离是多少？
21．（12分）（1）计算：①
； ②
.
（2）一个长方体木箱子，它的底是正方形，木箱高1.25米，体积2.718立方米．求这个木箱底边的长．（精确到0.01米）
22．（12分）如图，等腰梯形ABCD是一条河堤坝的横截面，AB∥DC，AE⊥CD于E，BF⊥CD，于F，AB＝3.5,AD＝3，AE＝2．求坝底DC的宽．（精确到0.1）
八年级数学参考答案
一、填空题：（每小题3分，共30分）
1．13；2．6；3．；4．
；5．3；6．
；7．8；8．0；9．0，±1，±2，±3；10．3．
二、选择题：（每小题3分，共24分）
| 题号 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 答案 | B | D | C | C | D | C | D | B |
三、解答题：
19．解：100cm.
20．解：10千米.
21．解：（1）①
；②
．（2）1.47米
22．解：8.0.