yuan7850
幼苗
共回答了15个问题采纳率:73.3% 举报
.(本小题满分14分)三棱柱
![](https://img.yulucn.com/upload/4/a0/4a0d5bd7ca43ea6a965b10cfd3802abd_thumb.jpg)
的直观图及三视图(主视图和俯视图是正方形,左侧图是等腰直角三角形)如图,
![](https://img.yulucn.com/upload/9/89/9890df5812532342590f0616658ca3fe_thumb.jpg)
为
![](https://img.yulucn.com/upload/5/15/5158709938999b202530bf23e4e15386_thumb.jpg)
的中点.
(1)求证:
![](https://img.yulucn.com/upload/9/c0/9c00c5708e5791aad64c127ec57f3fa6_thumb.jpg)
平面
![](https://img.yulucn.com/upload/3/66/3669747aa134d7b71672f91c682e9e50_thumb.jpg)
;
(2)求证:
![](https://img.yulucn.com/upload/6/53/6531c762142576710973608930207ead_thumb.jpg)
平面
![](https://img.yulucn.com/upload/3/66/3669747aa134d7b71672f91c682e9e50_thumb.jpg)
;
(3)求二面角
![](https://img.yulucn.com/upload/d/c9/dc9eb31c491fa885533074ac418d9efb_thumb.jpg)
的正切值.
解:由三视图可知,几何体为直三棱柱
![](https://img.yulucn.com/upload/2/f7/2f7a4f4903424bcd509f7ea1e36a72f8_thumb.jpg)
—
![](https://img.yulucn.com/upload/2/0e/20eeeff2afafa6b76b0f6036b536eea0_thumb.jpg)
,侧面
为边长为2的正方形,底面
![](https://img.yulucn.com/upload/2/f7/2f7a4f4903424bcd509f7ea1e36a72f8_thumb.jpg)
是等腰直角三角形,
![](https://img.yulucn.com/upload/a/59/a5939bae5b424488004b9a59ea5183df_thumb.jpg)
………2分(1)连BC交
![](https://img.yulucn.com/upload/8/c3/8c34f48da8a6253acfaec232150121f5_thumb.jpg)
于O,连接OD,在
![](https://img.yulucn.com/upload/d/24/d247f273fc45c00d7a3bb0ea1d408906_thumb.jpg)
中,O,D分别是
![](https://img.yulucn.com/upload/8/c3/8c34f48da8a6253acfaec232150121f5_thumb.jpg)
,
AC的中点,
而
![](https://img.yulucn.com/upload/9/74/9749b61b4857163d176fbe084d759b3b_thumb.jpg)
平面
![](https://img.yulucn.com/upload/3/66/3669747aa134d7b71672f91c682e9e50_thumb.jpg)
,
![](https://img.yulucn.com/upload/6/9f/69f22ed4ce5dcd974723c13576fd8b5b_thumb.jpg)
平面
![](https://img.yulucn.com/upload/3/66/3669747aa134d7b71672f91c682e9e50_thumb.jpg)
,
![](https://img.yulucn.com/upload/1/74/174536d8fc021257e57d152d23ccd457_thumb.jpg)
平面
![](https://img.yulucn.com/upload/3/66/3669747aa134d7b71672f91c682e9e50_thumb.jpg)
………………..4分
(2)直三棱柱
![](https://img.yulucn.com/upload/2/f7/2f7a4f4903424bcd509f7ea1e36a72f8_thumb.jpg)
—
![](https://img.yulucn.com/upload/2/0e/20eeeff2afafa6b76b0f6036b536eea0_thumb.jpg)
中,
![](https://img.yulucn.com/upload/9/39/939ffdb83b1c1819beb9599d6baee525_thumb.jpg)
平面
![](https://img.yulucn.com/upload/2/f7/2f7a4f4903424bcd509f7ea1e36a72f8_thumb.jpg)
,
![](https://img.yulucn.com/upload/8/ac/8ac0c659b89e41b32007fdddd8449d5f_thumb.jpg)
平面
![](https://img.yulucn.com/upload/2/f7/2f7a4f4903424bcd509f7ea1e36a72f8_thumb.jpg)
,
![](https://img.yulucn.com/upload/0/cb/0cb2e6ff6dadf3c0024e45408846237e_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/20/42086739eace200202fb528da45f72b3_thumb.jpg)
,D为AC的中点,
![](https://img.yulucn.com/upload/c/3e/c3e4b031452860a9df0142b4c1d5fce3_thumb.jpg)
,
![](https://img.yulucn.com/upload/6/50/65082076dbf09b43807eb468fd0a33d6_thumb.jpg)
平面
![](https://img.yulucn.com/upload/2/6f/26f3f76599db5113cfbbdf45369f092d_thumb.jpg)
,
![](https://img.yulucn.com/upload/0/28/0286d7a0137846ac51d5c3ac364f6418_thumb.jpg)
①………………..6分
又
![](https://img.yulucn.com/upload/c/05/c05ab74dc78c1355f6e03df779681b97_thumb.jpg)
,
在正方形
![](https://img.yulucn.com/upload/c/ba/cba75647f1f168f0012a973b86ea67bf_thumb.jpg)
②………………..8分
由①②,又
![](https://img.yulucn.com/upload/3/c7/3c70f9c8725cf2375832b0f3cf4094a2_thumb.jpg)
,
![](https://img.yulucn.com/upload/6/eb/6ebb8a866b9c963cb2245f8b76b09601_thumb.jpg)
……………………………………………………………9
![](https://img.yulucn.com/upload/5/d3/5d365c620b9ff2e6c99256361be12565_thumb.jpg)
(3)解法一;提示:所求二面角与二面角C-
![](https://img.yulucn.com/upload/4/3c/43ca38db2b91f27c0eedeb13592efe2a_thumb.jpg)
-D互余……………………………………..12
取BC中点H,有DH⊥平面
![](https://img.yulucn.com/upload/b/15/b156a8629684de44634f489928368aa9_thumb.jpg)
,过H作
![](https://img.yulucn.com/upload/4/3c/43ca38db2b91f27c0eedeb13592efe2a_thumb.jpg)
垂线,垂足为E,
![](https://img.yulucn.com/upload/7/a2/7a266a07438fdb6813cd22e147fd6ab4_thumb.jpg)
所以二面角C-
![](https://img.yulucn.com/upload/4/3c/43ca38db2b91f27c0eedeb13592efe2a_thumb.jpg)
-D的平面角是∠DEH…………….. ……………………12分
![](https://img.yulucn.com/upload/e/d0/ed0d64dc6495a5771a3e1b9b21c47189_thumb.jpg)
,因为二面角A-
![](https://img.yulucn.com/upload/4/3c/43ca38db2b91f27c0eedeb13592efe2a_thumb.jpg)
-D与二面角C-
![](https://img.yulucn.com/upload/4/3c/43ca38db2b91f27c0eedeb13592efe2a_thumb.jpg)
-
1年前
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