Trigonometric equations and inequalities
Difficulty: ★★☆
1776
Solve the equation: \(\sin 2x+\sqrt{2}\cos x=0\).
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Solution:
Use the formula \(\sin 2x=2\sin x\cos x\):
\(2\sin x\cos x+\sqrt{2}\cos x=0\).
Factor out \(\cos x\):
\(\cos x(2\sin x+\sqrt{2})=0\).
Hence:
1) \(\cos x=0\Rightarrow x=\dfrac{\pi}{2}+\pi n\), \(n\in\mathbb Z\).
2) \(2\sin x+\sqrt{2}=0\Rightarrow \sin x=-\dfrac{\sqrt{2}}{2}\).
Then \(x=-\dfrac{\pi}{4}+2\pi n\) or \(x=\dfrac{5\pi}{4}+2\pi n\), \(n\in\mathbb Z\).