在三角形A,B,C中,角A,B,C所对的边分别是a,b,c,cos(A+B)=-3/5 1在三角形A,B,C中,角A,B,C所对的边分别是a,b,c,cos(A+B)=-3/5 1.求cos2C-sin2C 的值 2.若a=5,三角形ABC的面积S=4,求c的值.
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![在三角形A,B,C中,角A,B,C所对的边分别是a,b,c,cos(A+B)=-3/5 1在三角形A,B,C中,角A,B,C所对的边分别是a,b,c,cos(A+B)=-3/5 1.求cos2C-sin2C 的值 2.若a=5,三角形ABC的面积S=4,求c的值.](/uploads/image/z/13350185-17-5.jpg?t=%E5%9C%A8%E4%B8%89%E8%A7%92%E5%BD%A2A%2CB%2CC%E4%B8%AD%2C%E8%A7%92A%2CB%2CC%E6%89%80%E5%AF%B9%E7%9A%84%E8%BE%B9%E5%88%86%E5%88%AB%E6%98%AFa%2Cb%2Cc%2Ccos%28A%2BB%29%3D-3%2F5+1%E5%9C%A8%E4%B8%89%E8%A7%92%E5%BD%A2A%2CB%2CC%E4%B8%AD%2C%E8%A7%92A%2CB%2CC%E6%89%80%E5%AF%B9%E7%9A%84%E8%BE%B9%E5%88%86%E5%88%AB%E6%98%AFa%2Cb%2Cc%2Ccos%28A%2BB%29%3D-3%2F5+1.%E6%B1%82cos2C-sin2C+%E7%9A%84%E5%80%BC+2.%E8%8B%A5a%3D5%2C%E4%B8%89%E8%A7%92%E5%BD%A2ABC%E7%9A%84%E9%9D%A2%E7%A7%AFS%3D4%2C%E6%B1%82c%E7%9A%84%E5%80%BC.)
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