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四棱锥S﹣ABCD的底面是边长为1的正方形,侧棱SB垂直于底面,并且SB=3,用α表示∠ASD,求sinα的值.
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解:因为SB垂直于底面ABCD,所以斜线段SA在底面上的射影为AB,由于DA⊥AB

所以DA⊥SA从而sinα=ADSD

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    When you're willing to ask for what you want but don't insist on getting it, there are some potential hidden benefits as well. For example, you sometimes 1 the sympathy and generosity in others.

    Several years ago, I arrived in Mumbai very late one evening. 2 having a confirmed reservation, the hotel was overbooked and was 3 people away. The man in front of me was angry and became very 4.

    He insisted on getting his way---but there were no 5. He stormed out, defeated and angry. He was totally 6 to the fact that it wasn't the receptionist's 7. It wasn't personal.

    I walked up to the receptionist and said8, “I really understand your9 and don't blame you a bit. I would 10 it so much if you would help me. I know you don't have any rooms here, but could you help me find another 11 close by?” I thought it was wise to ask---as long as I didn't 12.

    Hearing my words, she was 13. Remarkably, she said she had some great news, She had completely 14 that fact that one of the guests had to leave in an 15 and wouldn't be back. It turned out the most expensive room! Because I had been so 16, she gave it to me at lower rate.

    The question is, why didn't she 17 this empty room and give it to the angry man in front of me? I think the answer is pretty 18. His insistence pushed her away and may have even 19 to her “forgetfulness”. When I was talking to her, however, she relaxed and felt less 20. Her memory returned and I ended up getting a few hours of much-needed sleep.

    So be sure to ask for what you want, but don't insist on getting it.