如图，已知平面是正三角形，。 (Ⅰ)在线段上是否存在一点，使平面? (Ⅱ)求证：平面平面；(Ⅲ)求二面角的正切值。
— Look at the black clouds. It ＿＿ soon. — Sure. If only we ＿＿out.
I should very much like to have gone to that party of theirs, but ＿＿.
I want to buy that kind of cloth because I ＿＿ the cloth ＿＿ well.
— Can you give me the right answer? — Sorry, I ＿＿.Would you repeat that question?
— ＿＿you ＿＿ the editor at the airport? — No, he ＿＿ away before my arrival.
平面
是正三角
。
上是否存在一点
，使
平面
?
平面
；
的正切值。
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