Question 3 - A-Level Maths

Show that the equation $$5 \cos \theta - \sin \theta \tan \theta + 1 = 0$$ may be expressed in the form $a \cos ^ { 2 } \theta + b \cos \theta + c = 0$, where $a$, $b$ and $c$ are constants to be found.
Hence solve the equation $5 \cos \theta - \sin \theta \tan \theta + 1 = 0$ for $0 < \theta < 2 \pi$.