sin(70° a)cos(10° a)-cos(70° a)sin(170°-a)

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sin(70° a)cos(10° a)-cos(70° a)sin(170°-a)
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sin(70° a)cos(10° a)-cos(70° a)sin(170°-a)
sin(70° a)cos(10° a)-cos(70° a)sin(170°-a)

sin(70° a)cos(10° a)-cos(70° a)sin(170°-a)
sin 170度=sin (180度-10度)
=sin 10度,
sin(170°-a)=-sin170度=-sin10度
所以原式=sin(70° a)cos(10° a)+cos(70° a)sin(10° a)=sin(70° a+10° a)=sin80°a