sin5pai/6如何等于sin pai/6
sin(a\uff0dpai)\u7b49\u4e8e\u591a\u5c11 \u5728\u7ebf\u7b49\u89e3:sin(a\uff0dpai)=-sin(pai\uff0da)=-sin(a)
\u7531cos(\u963f\u6cd5\uff09=cos(-\u963f\u6cd5\uff09\u5f97 cos(\u963f\u6cd5-6\u5206\u4e4bpai)=cos(6\u5206\u4e4bpai-\u963f\u6cd5\uff09
cos(2\u5206\u4e4bpai-\u963f\u6cd5\uff09=sin\uff08\u963f\u6cd5\uff09 \u4e146\u5206\u4e4bpai-\u963f\u6cd5+\uff08\u963f\u6cd5+3\u5206\u4e4bpai\uff09=2\u5206\u4e4bpai
\u6240\u4ee5cos(6\u5206\u4e4bpai-\u963f\u6cd5\uff09=sin(\u963f\u6cd5+3\u5206\u4e4bpai)\uff1d3\u5206\u4e4b1
\u6545cos(\u963f\u6cd5-6\u5206\u4e4bpai)=3\u5206\u4e4b1
sin(5π/6)=sin[π-(π/6)]=sin(π/6)
根据y=sinx的曲线,可知sin(π-a)=sina
所以,sin5/6π=sin(π-5/6π)=sinπ/6
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绛旓細sin5鍏=sin锛4鍏+鍏锛=sin鍏=0
绛旓細鍥犱负Sina=y/X 5涓岀殑缁堣竟鍦▁杞翠笂锛寉=0 鎵浠ヤ负0
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