Mathematics - Trigonometric Ratios & Identities Question with Solution | TestHub

$\cos 5\theta =\cos (4\theta +\theta )=\cos 4\theta \cos \theta -\sin 4\theta \sin \theta =16{\cos }^5\theta -20{\cos }^3\theta +5\cos \theta$ Clearly $a=5,b=-20,c=16$ and $d=0$.