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根據積化和差公式cosa*sinb=(sin(a+b)-sin(a-b))/2 左邊=1/2(sin4x-sin(2x)=右邊所以成立 證明積化和差公式sin(a+b)-sin(a-b)=sianacosb + cosa sinb - sina cosb + cosa sinb =2cosa sinb 得證 積化和差以及和差化...
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