wji582
幼苗
共回答了15个问题采纳率:93.3% 举报
(1)见解析(2)45°
(1)以点 C 为原点, CB 、 CA 、 CC
1 所在直线为 x , y , z 轴,建立空间直角坐标系 C - xyz ,如图所示,
则 B (1,0,0), A (0,
![](https://img.yulucn.com/upload/c/d0/cd0e516497f24de825e67861e1a09d01_thumb.jpg)
,0), A
1 (0,
![](https://img.yulucn.com/upload/c/d0/cd0e516497f24de825e67861e1a09d01_thumb.jpg)
,
![](https://img.yulucn.com/upload/6/90/6909d7cde21e19cd919a8cd1e3e0b697_thumb.jpg)
), M
![](https://img.yulucn.com/upload/3/cb/3cb359e8115431bc82f2b42bc3e047e4_thumb.jpg)
.
所以
![](https://img.yulucn.com/upload/5/fb/5fb727f0386311fa8c477448d1a5832f_thumb.jpg)
=(1,-
![](https://img.yulucn.com/upload/c/d0/cd0e516497f24de825e67861e1a09d01_thumb.jpg)
,-
![](https://img.yulucn.com/upload/6/90/6909d7cde21e19cd919a8cd1e3e0b697_thumb.jpg)
),
![](https://img.yulucn.com/upload/c/c5/cc560389bcd5fc7e23400faaf6ccdf67_thumb.jpg)
=
![](https://img.yulucn.com/upload/4/7c/47c887af469eebc7aaaa9fcfda1c35d5_thumb.jpg)
.
因为
![](https://img.yulucn.com/upload/5/fb/5fb727f0386311fa8c477448d1a5832f_thumb.jpg)
·
![](https://img.yulucn.com/upload/c/c5/cc560389bcd5fc7e23400faaf6ccdf67_thumb.jpg)
=1×0+(-
![](https://img.yulucn.com/upload/c/d0/cd0e516497f24de825e67861e1a09d01_thumb.jpg)
)×(-
![](https://img.yulucn.com/upload/c/d0/cd0e516497f24de825e67861e1a09d01_thumb.jpg)
)+(-
![](https://img.yulucn.com/upload/6/90/6909d7cde21e19cd919a8cd1e3e0b697_thumb.jpg)
)×
![](https://img.yulucn.com/upload/e/e9/ee91ffe6c974c8af6d6c3bc8caf24a9e_thumb.jpg)
=0,所以 A
1 B ⊥ AM .
(2)因为 ABC A
1 B
1 C
1 是直三棱柱,所以 CC
1 ⊥平面 ABC ,又 BC ⊂平面 ABC ,所以 CC
1 ⊥ BC .
因为∠ ACB =90°,即 BC ⊥ AC ,又 AC ∩ CC
1 = C ,所以 BC ⊥平面 ACC
1 A
1 ,即 BC ⊥平面 AMC .
所以
![](https://img.yulucn.com/upload/c/2f/c2fe86bfdf7b319b825c240627a26a0d_thumb.jpg)
是平面 AMC 的一个法向量,
![](https://img.yulucn.com/upload/c/2f/c2fe86bfdf7b319b825c240627a26a0d_thumb.jpg)
=(1,0,0).
设 n =( x , y , z )是平面 BAM 的一个法向量,
![](https://img.yulucn.com/upload/9/da/9dafdb79c1753157cabea903313db576_thumb.jpg)
=(-1,
![](https://img.yulucn.com/upload/c/d0/cd0e516497f24de825e67861e1a09d01_thumb.jpg)
,0),
![](https://img.yulucn.com/upload/e/f9/ef956739bcb6d98b656b746b0ef5799e_thumb.jpg)
=
![](https://img.yulucn.com/upload/6/03/603f6dcf6c29b64878ee877f924b01fe_thumb.jpg)
.
由
![](https://img.yulucn.com/upload/1/a0/1a0756c478275603ea6d6bcb34b7f160_thumb.jpg)
得
![](https://img.yulucn.com/upload/0/89/089c95730463048ad44e7f4ccfe58682_thumb.jpg)
,令 z =2,得 x =
![](https://img.yulucn.com/upload/6/90/6909d7cde21e19cd919a8cd1e3e0b697_thumb.jpg)
, y =
![](https://img.yulucn.com/upload/3/34/334bf0f9f0a2dd6eefb1cd83fb597f18_thumb.jpg)
.
所以 n =(
![](https://img.yulucn.com/upload/6/90/6909d7cde21e19cd919a8cd1e3e0b697_thumb.jpg)
,
![](https://img.yulucn.com/upload/3/34/334bf0f9f0a2dd6eefb1cd83fb597f18_thumb.jpg)
,2)
因为|
![](https://img.yulucn.com/upload/c/2f/c2fe86bfdf7b319b825c240627a26a0d_thumb.jpg)
|=1,| n |=2
![](https://img.yulucn.com/upload/c/d0/cd0e516497f24de825e67861e1a09d01_thumb.jpg)
,所以cos〈
![](https://img.yulucn.com/upload/c/2f/c2fe86bfdf7b319b825c240627a26a0d_thumb.jpg)
, n 〉=
![](https://img.yulucn.com/upload/d/e2/de2385e8f5e9f53be512c4135863585f_thumb.jpg)
=
![](https://img.yulucn.com/upload/7/a8/7a818e69720176aa336e10ec29d22d89_thumb.jpg)
,
因此二面角 B AM C 的大小为45°
1年前
5