(i)[3]
Express $8\cos\theta - 15\sin\theta$ in the form $R\cos(\theta + \alpha)$, where $R > 0$ and $0^\circ < \alpha < 90^\circ$, and give the exact value of $R$ together with the value of $\alpha$ correct to 2 decimal places.
(ii)[4]
Hence solve $8\cos 2x - 15\sin 2x = 4$, for $0^\circ < x < 180^\circ$.