The equation of a curve is \(y = \sin x \sin 2x\). The curve has a stationary point in the interval \(0 < x < \frac{1}{2}\pi\).
Find the \(x\)-coordinate of this point, giving your answer correct to 3 significant figures.
Solution
To find the stationary point, we need to differentiate \(y = \sin x \sin 2x\) and set the derivative to zero.
Using the product rule, \(y' = \cos x \sin 2x + 2 \sin x \cos 2x\).
Using the double angle formula \(\sin 2x = 2 \sin x \cos x\), we can express the derivative in terms of \(\sin x\) and \(\cos x\).
Equating the derivative to zero, we obtain \(3 \sin^2 x = 2\), which simplifies to \(\tan^2 x = 2\).
Solving for \(x\), we find \(x = 0.955\) (to 3 significant figures).
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