Cho hình chóp S.ABCD có SA vuông với mp(ABCD), SA=2a, đáy là hình vuông ABCD cạnh = a, tâm O. Tính góc giữa SB và mp(SCD). Các cụ toán nhớ giải thích chi tiết giúp mình.

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V.  Combine each pair of sentences into one, using defining relative clauses and the  prompts provided. 21. In 1961, USPresident John Kennedy made a speech. It stared that Americans would land on the moon and be returned safely to the Earth.       In 1961 US President John Kennedy_________________________________________________   _________________________________________________________________________________       22. In 1959 NASA picked the first group of seven astronauts. They were called the “Mercury Seven”.       In 1952, NASA _________________________________________________________________ _________________________________________________________________________________                                                                                                                                                                           23. A spacesuit is made up of many parts. Aspacesuit help astronauts in many ways.       A spacesuit _____________________________________________________________________   _________________________________________________________________________________                                                                                                                                                                           24. In 1989, Helen Sharman went to Star City in Moscow. She spent 18 months of intensive training there.       In 1989, Helen Sharman ____________________________________________________________  _________________________________________________________________________________                                                                                                                                                                           25. Spacesuits also keep astronauts from getting hurt. Their visors protects eyes from bright sunlight.       Spacesuits________________________________________________________________________________________________________________________________________________________________