Period, maximum value and single-sine form of a combination of sin 4x and cos 4x

Period, maximum value and single-sine form of a combination of sin 4x and cos 4x

IB Year 6 | Grade 12
7 marks

The function \(\mathrm{g}\) is defined by \(\mathrm{g}(x)=8\sin4x-15\cos4x\) for \(x\in\mathbb{R}\).

  1. Determine the exact period of \(\mathrm{g}\).[2]
  2. Find the greatest value taken by \(\mathrm{g}(x)\).[1]
  3. It is given that \(\mathrm{g}(x)=R\sin(kx-\alpha)\), where \(R>0\), \(k>0\) and \(0<\alpha<\frac{\pi}{2}\).
    1. Find the value of \(R\).
    2. Write down the value of \(k\).
    3. Find the value of \(\alpha\).[4]

Solution:

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Answer:(a) \(\frac{\pi}{2}\) (b) \(17\) (c)(i) \(R=17\) (c)(ii) \(k=4\) (c)(iii) \(\alpha=\arctan\frac{15}{8}\approx1.08\)

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