Prove cosx+cos2x+cos3x=0
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solve it using the formulaes cos 2x = cos^x - sin ^x
cos3x = cos ^3 x - 3 sin^2 x cosx
put both these identities in the given expression, then all of them will cancel out each other and answer would be zero, as required
cos3x = cos ^3 x - 3 sin^2 x cosx
put both these identities in the given expression, then all of them will cancel out each other and answer would be zero, as required
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