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？

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．

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

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

16．····························································································································································· 一个数等于它的倒数的9倍，则这个数是··················································································································································· ( 　　)．

　　 (A)3　　　　　　　　　　 (B)　　　　　　　　　　 (C)±3　　　　 (D)±

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

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

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

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

11．····························································································································································· 的平方根是　 ( 　　)．

　　 (A)3　　　　　　　　　　 (B)±3　　　　　　　　　 (C)9　　　　　　　　　　 (D)±9