(cos2a+cos2c)/2

日期：2021-08-01 16:14:14 人气：1

(cos2a+cos2c)/2

(cos2A+cos2C)/2
=(2(cos((2A+2C)/2))(cos((2A-2C)/2)))/2
=(cos(A+C))(cos(2A-2C))
(cos A)+(cos B)=2*(cos(A+B)/2)(cos(A-B)/2)
    A+
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