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。
He said that he would pass the exam and this ________ to be true.（ ）
turned out
put out
broke out
tried out
﹣﹣﹣We can always find something good in a bad ________ if we look for it.
﹣﹣﹣ It's so true.Let's make full use of what comes.（ ）
situation
direction
instruction
competition
In many countries，people put their fingers up to their mouths ________ silence.（ ）
ask for
asking for
to ask for
asked for
﹣﹣﹣ How did you come to Baoying？
﹣﹣﹣By high﹣speed rail.It ________ me only 28 minutes to get here.（ ）
spent
paid
lost
took
We ________ see which way to go if the stars do not twinkle（闪耀）so.（ ）
can not
should not
must not
need not
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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