三角形ABC中 tanC=3倍的根号7 (1)求cosC (2)若向量CB乘以向量CA=5/2 且a+b=9 求c1,cosC=1/8;把C当作一个直角三角形的锐角顶点即可,对边为3倍根号7,临边为1,则斜边为8;(原本的ABC不一定是直角三
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![三角形ABC中 tanC=3倍的根号7 (1)求cosC (2)若向量CB乘以向量CA=5/2 且a+b=9 求c1,cosC=1/8;把C当作一个直角三角形的锐角顶点即可,对边为3倍根号7,临边为1,则斜边为8;(原本的ABC不一定是直角三](/uploads/image/z/1600645-13-5.jpg?t=%E4%B8%89%E8%A7%92%E5%BD%A2ABC%E4%B8%AD+tanC%3D3%E5%80%8D%E7%9A%84%E6%A0%B9%E5%8F%B77+%EF%BC%881%EF%BC%89%E6%B1%82cosC+%EF%BC%882%EF%BC%89%E8%8B%A5%E5%90%91%E9%87%8FCB%E4%B9%98%E4%BB%A5%E5%90%91%E9%87%8FCA%3D5%2F2+%E4%B8%94a%2Bb%3D9+%E6%B1%82c1%2CcosC%3D1%2F8%3B%E6%8A%8AC%E5%BD%93%E4%BD%9C%E4%B8%80%E4%B8%AA%E7%9B%B4%E8%A7%92%E4%B8%89%E8%A7%92%E5%BD%A2%E7%9A%84%E9%94%90%E8%A7%92%E9%A1%B6%E7%82%B9%E5%8D%B3%E5%8F%AF%2C%E5%AF%B9%E8%BE%B9%E4%B8%BA3%E5%80%8D%E6%A0%B9%E5%8F%B77%2C%E4%B8%B4%E8%BE%B9%E4%B8%BA1%2C%E5%88%99%E6%96%9C%E8%BE%B9%E4%B8%BA8%EF%BC%9B%EF%BC%88%E5%8E%9F%E6%9C%AC%E7%9A%84ABC%E4%B8%8D%E4%B8%80%E5%AE%9A%E6%98%AF%E7%9B%B4%E8%A7%92%E4%B8%89)
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