Trigonometry - Trigonometric Equations

Trigonometry - Trigonometric Equations

The diagram shows four points \(A\), \(B\), \(C\) and \(O\) such that that \(AB = 2\) m, \(BC = 10\) m,
\(\angle AOC = \angle ABC = 90{}^\circ\) and \(\angle OCB = \theta{}^\circ\).

  1. Show that \(OC = 2\sin \theta + 10\cos \theta\).
  2. Express \(OC\) in the form \(R\sin(\theta + \alpha)\).
  3. Find the maximum value of \(OC\) and the corresponding value of \(\theta\).
  4. Find the value of \(\theta\) for which \(OC = 8\) m.

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Answer:(a) \(OC=2\sin\theta+10\cos\theta\) (b) \(OC=2\sqrt{26}\sin(\theta+78.7^\circ)\) (c) \(OC_{\max}=2\sqrt{26}\text{ m}\) when \(\theta=11.3^\circ\) (d) \(\theta=49.6^\circ\)

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