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How do you evaluate $2 cos^2 (pi/12) - 1$ ?

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Konstantinos Michailidis

May 15, 2016

We know that $cos(2x)=2cos^2(x)-1$

Hence for $x=pi/12$ we have that

$2cos^2(pi/12)-1=cos(2*pi/12)=cos(pi/6)=sqrt3/2$

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