求sin15°+cos165°的值

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求sin15°+cos165°的值
求sin15°+cos165°的值

求sin15°+cos165°的值
原式= sin 15° +cos (180° -15°)
= sin 15° -cos 15°
= (根号2) [ (根号2)/2 *sin 15° - (根号2)/2 *cos 15° ]
= (根号2) ( sin 15° cos 45° -cos 15° sin 45°)
= (根号2) sin (-30°)
= - (根号2) sin 30°
= - (根号2) /2.
= = = = = = = = =
已用计算器验证.

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