(12分) 22.已知四棱錐P-ABCD的底面為直角梯形,AB∥DC,
底面ABCD,PA=AD=DC=
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AB=1,M是PB的中點(diǎn)
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(Ⅰ)證明:面PAD⊥面PCD;
(Ⅱ)求異面直線CM與AD所成角的正切值;
(Ⅲ)求面MAC與面BAC所成二面角的正切值
(1)略 (2)
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(3)
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本題考查證明面面垂直的方法,求線線角即二面角的方法,關(guān)鍵是進(jìn)行等價(jià)轉(zhuǎn)化.
(1)先證明平面PAD⊥平面ABCD,再證得CD⊥平面PAD即可得到平面PAD⊥平面PCD.
(2)BP中點(diǎn)M,采用平移法得到異面直線的所成的角。
(3)根據(jù)三垂線定理可得二面角M-AC-B的平面角,解直角三角形求此角的大�。�
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,
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是
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外一點(diǎn),過點(diǎn)
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與
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分別交于
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在正方體
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設(shè)
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表示不同的直線,
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表示不同的平面,給出下列四個(gè)命題:
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∥
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,且
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則
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;
②若
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∥
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,且
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∥
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.則
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∥
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;
③若
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,則
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∥m∥n;
④若
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且n∥
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,則
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∥m.
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