tan12 cot38 cot52 cot 60 cot78
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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)
you can change and do it
= 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)
you can change and do it
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