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# Write the given term $\cos 4\theta$ in terms of $\cos \theta$.

Last updated date: 15th Mar 2023
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Hint: Start by splitting the given terms and then apply the formula of $\cos 2\theta$ in the above equation.
We have, $\cos 4\theta$, we can apply the formula of $\cos 2\theta = 2{\cos ^2}\theta - 1$,
$\cos 4\theta = 2{\cos ^2}2\theta - 1$
$\cos 4\theta = 2{\left( {2{{\cos }^2}\theta - 1} \right)^2} - 1$
$\cos 4\theta = 8{\cos ^4}\theta - 8{\cos ^2}\theta + 1$