If \(\cos \theta \neq 0\), and \(\sec \theta-1=(\sqrt{2}-1) \tan \theta\) then \(\theta=\)

If \(\cos \theta \neq 0\), and \(\sec \theta-1=(\sqrt{2}-1) \tan \theta\) then \(\theta=\)
  1. \(n \pi+\frac{\pi}{8}, n \in Z\)
  2. \(2 n \pi+\frac{\pi}{4}\) or \(2 n \pi, n \in Z\)
  3. \(2 n \pi+\frac{\pi}{8}, n \in Z\)
  4. \(2 n \pi-\frac{\pi}{4}\) or \(2 n \pi, n \in Z\)

Solution

If \(\cos \theta \neq 0\) and \(\sec \theta-1=(\sqrt{2}-1) \tan \theta\) \(\begin{array}{ll} \Rightarrow \quad \frac{1-\cos \theta}{\cos \theta}=(\sqrt{2}-1) \frac{\sin \theta}{\cos \theta} \\ \Rightarrow \quad 2 \sin ^2 \frac{\theta}{2}=(\sqrt{2}-1) 2 \sin \frac{\theta}{2} \cos \frac{\theta}{2} \end{array}\) \(\Rightarrow \text{Either } \sin \frac{\theta}{2}=0 \text { or } \tan \frac{\theta}{2}=\sqrt{2}-1\) \(\Rightarrow \text{Either } \frac{\theta}{2}=n \pi, n \in Z\) \(\text{or } \frac{\theta}{2}=n \pi+\frac{\pi}{8}, n \in Z\) \(\Rightarrow \quad \theta=2 n \pi+\frac{\pi}{4}\) or \(2 n \pi, n \in Z\) Hence, option (2) is correct.

Asked in: AP EAMCET 2019 (20 Apr Shift 1)

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