Question #ce9db

1 Answer

Aug 16, 2016

$cos 3theta=44/125=0.352$

Explanation:

$sin theta=3/5 ; cos theta=sqrt(1-(3/5)^2)=4/5$
$costheta =-4/5$ when $theta$ is in between $90^0 & 180^0$
$cos 3theta=4cos^3theta-3costheta= 4*(-4/5)^3-3*(-4/5) = -256/125+12/5=44/125=0.352$ [Ans]

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Question #ce9db

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