9709 P3 - Nov 2008 - Q6 - 8 marks
170
(i) Express \(5 \sin x + 12 \cos x\) in the form \(R \sin(x + \alpha)\), where \(R > 0\) and \(0^\circ < \alpha < 90^\circ\), giving the value of \(\alpha\) correct to 2 decimal places.
(ii) Hence solve the equation \(5 \sin 2\theta + 12 \cos 2\theta = 11\), giving all solutions in the interval \(0^\circ < \theta < 180^\circ\).
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