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According to de Moivre's formula,

cos3x + isin3x = (cosx + isinx)3 = cos3x + 3cos2x*isinx + 3cosx*i2sin2x + i3sin3x

Comparing the imaginary parts,

isin3x = 3cos2x*isinx + i3sin3x

so that sin3x = 3cos2x*sinx - sin3x

= 3*(1-sin2x)sinx - sin3x

= 3sinx - 4sin3x

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Q: How do you express sin 3x as a polynom with sin x using the De Moivre formula?
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