sina+sinb=2sin(1/2a+1/2b)cos(1/2a-1/2b)怎么来的啊?
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sina+sinb=2sin(1/2a+1/2b)cos(1/2a-1/2b)怎么来的啊?
sina+sinb
=sin[(1/2a+1/2b)+(1/2a-1/2b)]+sin[(1/2a+1/2b)-(1/2a-1/2b)]
=sin(1/2a+1/2b)cos(1/2a-1/2b)+cos(1/2a+1/2b)sin(1/2a-1/2b)+sin(1/2a+1/2b)cos(1/2a-1/2b)-cos(1/2a+1/2b)sin(1/2a-1/2b)
=2sin(1/2a+1/2b)cos(1/2a-1/2b)
即
sina+sinb=2sin(1/2a+1/2b)cos(1/2a-1/2b)
得证
=sin[(1/2a+1/2b)+(1/2a-1/2b)]+sin[(1/2a+1/2b)-(1/2a-1/2b)]
=sin(1/2a+1/2b)cos(1/2a-1/2b)+cos(1/2a+1/2b)sin(1/2a-1/2b)+sin(1/2a+1/2b)cos(1/2a-1/2b)-cos(1/2a+1/2b)sin(1/2a-1/2b)
=2sin(1/2a+1/2b)cos(1/2a-1/2b)
即
sina+sinb=2sin(1/2a+1/2b)cos(1/2a-1/2b)
得证
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