www.fltk.net > 求证Cos7x+7Cos5x+21Cos3x+35Cosx=64Cos^7x

求证Cos7x+7Cos5x+21Cos3x+35Cosx=64Cos^7x

证明: cos3x=4(cosx)^3-3cosx 4(cosx)^3=cos3x+3cosx 16(cosx)^6=(cos3x)^2+6cos3xcosx+9(cosx)^2 =(1+cos6x)/2+3(cos4x+cos2x)+9/2*(1+cos2x) 32(cosx)^6=1+cos6x+6cos4x+6cos2x+9+9cos2x 64(cosx)^7=2cos6xcosx+12cos4xcosx+30cos2xcosx+20cos...

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