(1)设S=sinx+sin3x+sin5x+.+sin(2n-1)xS=sin(2n-1)x+sin(2n-3)x+.+sinx上下对应项相加得(和差化积):2S=2sin(nx)cos(n-1)x+2sin(nx)cos(n-3)x+.+2sin(nx)cos(n-3)x+2sin(nx)cos(n-1)xS=sin(nx)[cos(n-1)x+cos(n-3)x+....
sinx+sin3x+sin5x+.sin(2n-1)/cosx+cos3x+cos5x+.cos(2n-1)= sin
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