是化简这个2cos(A+B)cosA-cos(2A+B)吧
2cos(A+B)cosA-cos(2A+B)
=2cos(A+B)cosA-cos(A+A+B)
=2cos(A+B)cosA-[cosAcos(A+B)-sinAsin(A+B)]
=cosAcos(A+B)+sinAsin(A+B)
=cos[A-(A+B)]
=cos(-B)
=cosB
如果不是直接用Hi再问吧.
化简：2cos(A+B)cosB-cos(2A+B)
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