Sin(x–18°)怎么变成sin(18°-x) sin(x＋27°)cos(18°－x)－sin(63°－x...
YSin(x\u201318\u00b0)\u600e\u4e48\u53d8\u6210sin(18\u00b0-x)sin(x)\u662f\u5947\u51fd\u6570\uff0c\u6240\u4ee5 y\u00d7sin(x\u201318\u00b0)\uff1d-y\u00d7sin(18\u00b0-x)
sin(x-27\u00b0)cos(18\u00b0-x)-sin(\u301063\u00b0\u3011-x)sin(x-18\u00b0)
=sin(x+27\u00b0)cos(18\u00b0-x)+cos(90\u00b0-\u301063\u00b0-x\u3011)sin(18\u00b0-x)
=sin(x+27\u00b0)cos(18\u00b0-x)+cos(90\u00b0-63\u00b0+x)sin(18\u00b0-x)
=sin(x+27\u00b0)cos(18\u00b0-x)+cos(27\u00b0+x)sin(18\u00b0-x)
=sin45\u00b0
=\u221a2/2
sin(x-18°)=sin[-(18°-x)]=-sin(18°-x)
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