(a)[3]
Show that the equation $5\cos\theta - \sin\theta\tan\theta + 1 = 0$ can be rewritten in the form $a\cos^2\theta + b\cos\theta + c = 0$, where $a$, $b$ and $c$ are constants to be found.
(b)[4]
Hence solve the equation $5\cos\theta - \sin\theta\tan\theta + 1 = 0$ for $0 < \theta < 2\pi$.