SNOW想飛
幼苗
共回答了13个问题采纳率:69.2% 举报
(1)取PA的中点E,连接BE、EM,则EM与BC平行且相等,
∴四边形BCME是平行四边形.
∴MC∥BE,
又MC
![](https://img.yulucn.com/upload/6/ae/6ae5d87edda005488c78f577cb3f877b_thumb.jpg)
面PAB,BE
![](https://img.yulucn.com/upload/5/0c/50c7e5717062810ae2fb7657bf0dfae7_thumb.jpg)
面PAB,
∴MC∥平面PAB
(2)如图过Q作QF∥PA交AD于F,
∴QF⊥平面ABCD.作FH⊥AC,H为垂足.连接QH
∴∠QHF是二面角Q﹣AC﹣D的平面角.
设AF=x,
∴AH=FH=
![](https://img.yulucn.com/upload/f/39/f39468198d1d2fcb9fecff5e412b959b_thumb.jpg)
x,FD=2﹣x.
又
![](https://img.yulucn.com/upload/a/b7/ab7bda4774a0dad970ea79385be7a6c3_thumb.jpg)
=
![](https://img.yulucn.com/upload/c/bd/cbd85c404f3b37cbdb3c7876a33398d9_thumb.jpg)
,
∴QF=
![](https://img.yulucn.com/upload/0/4c/04cb57a720c41fbdc0e9f635d92133d1_thumb.jpg)
,
在Rt△QFH中,tan∠QHF=
![](https://img.yulucn.com/upload/b/c7/bc752b1d7c532606373871967e6a4645_thumb.jpg)
=
![](https://img.yulucn.com/upload/5/7d/57d84426d56edd4e87a814085f6a2f56_thumb.jpg)
=
![](https://img.yulucn.com/upload/f/1a/f1a8ed9e429310868f6bf0f19f858e91_thumb.jpg)
,
∴x=1.
当Q为棱PD中点时,二面角Q﹣AC﹣D的正切值为
![](https://img.yulucn.com/upload/b/0e/b0e8877e63af71f9a2107e4c360e9873_thumb.jpg)
.
1年前
6