解答题-证明题 较易0.85 引用1 组卷271
如图,在三棱锥
中,
,∠ACB=90°,侧面
为等边三角形,侧棱
.
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/864aba4443da435d9f7ef0f795ef21bf.png?resizew=192)
(Ⅰ)求证:
;
(Ⅱ)求证:平面PAB⊥平面
;
(Ⅲ)求二面角
的余弦值.
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/51cff678414d4c2ead3da54d7ead8c87.png?resizew=60)
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/b955bbc11e174293b12f5ea8a6b349c7.png?resizew=95)
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/cf7607dbc8d3463f84a9d239460a264f.png?resizew=35)
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/07a320938e9a4c278854a6ad4dd82ee7.png?resizew=73)
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/864aba4443da435d9f7ef0f795ef21bf.png?resizew=192)
(Ⅰ)求证:
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/ddaef9387bb74310a296a8b9ed59fe67.png?resizew=62)
(Ⅱ)求证:平面PAB⊥平面
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/2536f3feeab34ea79d0179f1db96b3b7.png?resizew=37)
(Ⅲ)求二面角
![](https://img.xkw.com/dksih/QBM/2016/8/3/1572950095380480/1572950101630976/STEM/bcb965000a0d49a1b96e78b91ee56675.png?resizew=74)
15-16高二下·广东·期中
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