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如图.在底面为直角梯形的四棱锥P-ABCD中.AD∥BC.∠ABC=90°.PA⊥平面AB
如图.在底面为直角梯形的四棱锥P-ABCD中.AD∥BC.∠ABC=90°.PA⊥平面AB
发布时间:2021-02-20 21:58:08
如图,在底面为直角梯形的四棱锥P-ABCD中,AD∥BC,∠ABC=90°,PA⊥平面ABCD,PA=4,AD=2,AB=2
3,BC=6.(Ⅰ)求证:BD⊥平面PAC;(Ⅱ)求二面角A-PC-D的大小.
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答案:
分析:
(Ⅰ)要证BD⊥平面PAC,只需证明BD垂直平面PAC内的两条相交直线PA,AC即可.
(Ⅱ)过E作EF⊥PC,垂足为F,连接DF,说明∠EFD为二面角A-PC-D的平面角,推出Rt△EFC∽Rt△PAC,通过解Rt△EFD,求二面角A-PC-D的大小.
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