Question

please tell me the formula of cot(3x)

Answer 1

cos 3x = cos(2x+x)

= cos(2x).cos(x) - sin(2x).sin(x)

= {2cos^2 (x) - 1}.cos(x) - {(2sin(x).cos(x)}.sin(x)

= cos(x) {2cos^2 (x) - 1 - 2sin^2 (x)}

=cos(x) {2cos^2 (x) - 1 - 2(1 - cos^2 (x))}

=cos(x) {2cos^2 (x) - 1 - 2 + 2cos^2 (x)}

=cos(x) {4cos^2 (x) - 3}

=4cos^3 (x) - 3cos(x)

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Answer 2

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