1 . 如图,在四棱柱
中,
底面
,
为线段
上的任意一点(不包括
两点),平面
与平面
交于
.
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/671c7bd6d97d4a0a9108b08e28980c0c.png)
(1)证明:
;
(2)证明:
平面
.
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/631952a9f2de437b9faac647ed40c711.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/641b0ade8ec743e7987d856a314da73e.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/ec2b4dcdfc384a2eb7e1f8002eff968d.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/ec84e065d7f6455bae3d6713e8c8e33a.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/b761957941bf4df99b2f3d03063ae05a.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/fe8a5935342e486d82fbb00babb6cbe0.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/7335b4b0e254408aab25f1bd24801c5b.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/a782eb0f4fb9401bb37abd663e0b0563.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/55987375be014074ace739f3540cea4f.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/671c7bd6d97d4a0a9108b08e28980c0c.png)
(1)证明:
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/4b45e734ac664a649faddcdb845aa96d.png)
(2)证明:
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/3b12e727040d48b9b3fee022040634ca.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017403351040/1573017409118208/STEM/e900fc5bf7a144128652ac643e83dd28.png)
您最近一年使用:0次
2 . 如图,已知四棱台
的上下底面分别是边长为3和6的正方形,
,且
底面
,点
分别在棱
上,且
,
.
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/df69a4cc6b21400c9444d54793c83caa.png)
(1)证明:
平面
;
(2)求二面角
的余弦值.
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/cf729744c209450d99dc6e82207fbaa6.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/6449a9b75825441bafd70c3f6fedb3f3.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/40a60ba8b5f6423a80e2ee0d30547a82.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/643e70407f4245da9c118f9b267878c8.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/6e32feadc40a4aa6a3cc3ea2c3e7b605.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/2250b776f4154233b9e752151083ea55.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/0ca1497baca04c4e853b716cf64f1c8a.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/9e58f0da1bff4546aba156416bb9e9ad.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/df69a4cc6b21400c9444d54793c83caa.png)
(1)证明:
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/8890e3bf96af4c00a13875ca90406b2c.png)
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/eee1cb962a294bc2b381da70ed12b670.png)
(2)求二面角
![](https://img.xkw.com/dksih/QBM/2016/9/13/1573017246253056/1573017252577280/STEM/08cb9e104beb4d238dc33d2d77513bd5.png)
您最近一年使用:0次