Find the value of $cos2theta$ for $theta=pi/4$ ?

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Answer 1 · 2016-11-13T17:09:39

$cos2theta=0$

$cos2theta=cos(theta+theta)$

= $costhetaxxcostheta-sinthetaxxsintheta$

as for $theta=pi/4$ , $costheta=sintheta=1/sqrt2$

$cos2theta=costhetaxxcostheta-sinthetaxxsintheta$

= $1/sqrt2xx1/sqrt2-1/sqrt2xx1/sqrt2$

= $1/2-1/2=0$

Find the value of cos2thetacos2theta for theta=pi/4theta=pi/4?