cos（α-35°）cos（α+25°）+sin（α-35°）sin（α+25°）怎么算
问题描述：
cos（α-35°）cos（α+25°）+sin（α-35°）sin（α+25°）怎么算
答
原式 = cos [ (α -35°) -(α +25°) ]
= cos (-60°)
= cos 60°
= 1/2.
= = = = = = = = =
cos (A-B) =cos A cos B +sin A sin B,
cos (-A) =cos A.