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【330506】第2章检测题及答案解析

时间:2025-02-09 11:35:35 作者: 字数:8563字

2 四边形检测题

(本检测题满分:100分,时间:90分钟)

一、选择题(每小题3分,共24分)

1.下面图形中,既是轴对称图形又是中心对称图形的是(

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

2.如图所示,在  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的垂直平分线交 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 于点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,则△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长是(

A.6 B.8 C.9 D.10

3.如图所示,在矩形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 分别为边 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的中点. <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,则图中阴影部分的面积为(

A.3 B.4 C.6 D.8

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

Group 479






4 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .如图为菱形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 与△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 重叠的情形,其中 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 上.若 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,则 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

A.8 B.9 C.11 D.12

5. (2015•江苏连云港中考)已知四边形ABCD,下列说法正确的 ( )

A.ADBCABDC时,四边形ABCD是平行四边形

B.ADBCABDC时,四边形ABCD是平行四边形

C.ACBDAC平分BD时,四边形ABCD是矩形

D.ACBDACBD时,四边形ABCD是正方形

6. 2015·湖北孝感中考)已知一个正多边形的每个外角等于60°,则这个正多边形是(

A.正五边形 B.正六边形 C.正七边形 D.正八边形

7.若正方形的对角线长为2 cm,则这个正方形的面积为(

A <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .4  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> B.2 C. <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> D.

82015·贵州安顺中考)如图,点O是矩形ABCD的中心,EAB上的点,折叠后,点B恰好与点O重合,若BC=3,则折痕CE的长为(

A

8题图

.2 B. <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

C. D.6


二、填空题(每小题3分,共24分)

9.如图,在ABCD中,已知 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,那么 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> _____ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ______ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

10.如图,在 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 分别为边 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的中点,则图中共有 个平行四边形.

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>


Group 292




11. 2015•湖北襄阳中考)在ABCD中,AD=BD,BEAD边上的高,∠EBD=20°,

A的度数为_________.

12.如图,在△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中,点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 分别是 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的中点, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,则

C的度数为________.


 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>






13题图



                           

13.2015·上海中考)已知E是正方形ABCD的对角线AC上一点,AEAD,过点EAC的垂线,交边CD于点F,那么FAD________

14.若凸 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 边形的内角和为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,则从一个顶点出发引出的对角线条数是__________.

15.如图所示,在矩形ABCD中,对角线 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 相交于点O,且 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,则BD的长为_____cmBC的长为_____cm.

16.如图所示,在菱形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中,对角线 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 相交于点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的中点,已知 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,则 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ______ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

Group 698


Group 296







三、解答题(共52分)

17.6分)已知 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长为40 cm <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,求 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的长.

18.6分)已知, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的平分线分 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 两条线段,求 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长.

19.6分)如图所示,四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是平行四边形, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,求 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的长.

Group 578  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>







20.6分)如图所示,在矩形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 相交于点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 平分 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 于点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .若 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,求 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的度数.

21.6分)如图所示, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 点是正方形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 边上任意一点, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 点并交 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 边于 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 点,以点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 为中心,把△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 顺时针旋转 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 得到△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .试说明: <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 平分∠ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

22.(6) 如图,在Rt <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中,∠C=90°,∠B=60° <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> EF分别为边ACAB的中点.

1)求∠A的度数;

2)求 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的长.

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

23.(8)已知:如图,四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是菱形,过 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的中点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的垂线 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,交 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 于点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的延长线于点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

1)求证: <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

2)若 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,求菱形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长.

24.(8)如图,M是△ABC的边BC的中点,AN平分∠BACBNAN于点N,延长BNAC于点D,已知AB=10BC=15MN=3.

1)求证:BN=DN

2)求△ABC的周长.

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

Group 644










2 四边形检测题参考答案

1.C 解析:选项AB是中心对称图形但不是轴对称图形,选项C既是中心对称图形又是轴对称图形,选项D是轴对称图形但不是中心对称图形.

2.B 解析:在平行四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的垂直平分线交 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 于点 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

3.B 解析:因为矩形ABCD的面积为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以阴影部分的面积为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,故选B

4 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .D 解析:连接 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,设 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

因为四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 为菱形,

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,且 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

在△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中,因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以.

在△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中,因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

故选D

5. 解析:一组对边平行,另一组对边相等的四边形可能是等腰梯形,故A项错误;两组对边分别相等的四边形一定是平行四边形,故B项正确;对角线相等且一条对角线平分另一条对角线的四边形不一定是矩形,故C项错误;对角线相等且互相垂直的四边形不一定是正方形,故D项错误.

6.B 解析:设正多边形为n边形,因为正多边形的外角和为360°,所以n=  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

7Group 720 .B 解析:如图所示,在正方形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以正方形的面积为2  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,故选B.

8. 解析根据图形折叠的性质可得:BCE=ACE= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ACB

B=COE=90°BC=CO= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> AC,所以BAC=30°

所以BCE=ACE= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ACB=30°.因为BC=3,所以CE=2 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

9. <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 12 解析:因为四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是平行四边形,

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

又因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

10.4 解析:因为在ABCD中,EF分别为边ABDC的中点,所以  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

ABCD,所以四边形AEFDCFEBDFBE都是平行四边形,再加上ABCD本身,共有4个平行四边形,故答案为4

11.55°35° 解析: 当高BE的垂足在AD上时,如图(1),


 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

11题答图(1

ADB=90°-20°=70°.AD=BD得到∠A=DBA= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> =55°.

当垂足EAD的延长线上时,如图(2),

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

11题答图(2

BDE=90°-20°=70°,则∠ADB=110°,

AD=BD得到∠A=ABD= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> =35°.

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .


12. <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 解析:由题意,得 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

DE分别是ABAC的中点,∴ DE是△ABC的中位线,

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,∴  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

13. 22.5° 解析:由四边形ABCD是正方形,可知BAD=D=90°

CAD= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> BAD=45°.

FEAC,可知AEF=90°.

RtAEFRtADF中,AE=ADAF=AF

RtAEFRtADFHL),

FAD=FAE= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> CAD= <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ×45°=22.5°

14.6 解析:由题意,得 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 解得 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 这个多边形为九边形,所以从九边形的一个顶点引出的对角线条数为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

15.4  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 解析:因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> cm,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> cm.又因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> cm.

,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> cm.

16. <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 解析:∵ 四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是菱形,  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

又∵  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

Rt <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 中,由勾股定理,得 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的中点, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的中位线,  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

17.解:因为四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是平行四边形,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> cm <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> cm

又因为平行四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长为40 cm

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,解得 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

18.解:设∠ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的平分线交 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 点,如图所示.

Group 730 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以∠ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

又∠ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以∠ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

① <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 时, <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

19.解:因为四边形ABCD是平行四边形,

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的长分别为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

20.解:因为  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 平分 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

又知 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 为等边三角形,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 为等腰直角三角形,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,此时 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

21.解:因为△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 顺时针旋转 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 得到△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ≌△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,即 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 平分∠ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

22.:(1)∵ RtABC中,∠C=90°,∠B=60°

∴∠A=90° <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> B=30°,即∠A的度数是30°.

2)由(1)知,∠A=30°

RtABC中,∠C=90°,∠A=30°AB=8 cm

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

EF分别为边ACAB的中点,

EF是△ABC的中位线,

 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

23.1)证明:因为四边形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是菱形,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

又因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的垂直平分线,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .(2)解:因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>  <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .

又因为 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> ,所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以△ <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 是等腰三角形,

所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> .所以 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

所以菱形 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a> 的周长是 <a href="/tags/46/" title="答案" class="c1" target="_blank">答案</a>

24.1)证明:在△ABN和△ADN中,

1=∠2 ANAN ,∠ANB=∠AND

ABN≌△ADN,∴ BN= DN

2)解:∵ ABN≌△ADN,∴ AD=AB=10DN=NB.

又∵点MBC的中点,∴ MN是△BDC的中位线,

CD=2MN=6,故△ABC的周长=AB+BC+CD+AD=10+15+6+10=41