化简:sin7°+cos15°sin8°cos7°−sin15°sin8°.
问题描述:
化简:
. sin7°+cos15°sin8° cos7°−sin15°sin8°
答
因为cos15°sin8°=12[sin(8°+15°)+sin(8°-15°)=12(sin23°-sin7°)],sin15°sin8°=12(cos7°-cos23°),所以sin7°+cos15°sin8°cos7°−sin15°sin8°=sin23°+sin7°cos23°+cos7°=2sin15°cos8...