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Problem 527
527
(i) Sketch and label, on the same diagram, the graphs of \(y = 2 \sin x\) and \(y = \cos 2x\), for the interval \(0 \leq x \leq \pi\).
(ii) Hence state the number of solutions of the equation \(2 \sin x = \cos 2x\) in the interval \(0 \leq x \leq \pi\).
Solution
(i) To sketch the graphs of \(y = 2 \sin x\) and \(y = \cos 2x\) for \(0 \leq x \leq \pi\):
- The graph of \(y = 2 \sin x\) will have a maximum value of 2 and a minimum value of 0 within the interval. It completes half a cycle from 0 to \(\pi\).
- The graph of \(y = \cos 2x\) completes a full cycle from 0 to \(\pi\), oscillating between 1 and -1.
(ii) The number of solutions to \(2 \sin x = \cos 2x\) corresponds to the number of intersection points of the two graphs within the interval \(0 \leq x \leq \pi\). From the sketch, there are 2 points of intersection.