In $(0,2 \pi)$, the number of solutions of $\tan \theta+\sec \theta=2 \cos \theta$ are

In $(0,2 \pi)$, the number of solutions of $\tan \theta+\sec \theta=2 \cos \theta$ are
  1. 0
  2. 1
  3. 2
  4. 3

Solution

$\begin{aligned} & \tan \theta+\sec \theta=2 \cos \theta \\ & \Rightarrow \frac{\sin \theta}{\cos \theta}+\frac{1}{\cos \theta}=2 \cos \theta \\ & \Rightarrow \sin \theta+1=2 \cos ^2 \theta \\ & \Rightarrow \sin \theta+1=2\left(1-\sin ^2 \theta\right) \\ & \Rightarrow 2 \sin ^2 \theta+\sin \theta-1=0\end{aligned}$ $\begin{aligned} \therefore \quad \sin \theta= & -1, \frac{1}{2} \\ \text { For } \sin \theta & =-1, \sin \theta=\frac{1}{2} \\ \theta & =\frac{3 \pi}{2} \quad \theta=\frac{\pi}{6}, \frac{5 \pi}{6} \end{aligned}$ $\therefore \quad$ Number of solutions $=3$

Asked in: MHT CET 2024 (09 May Shift 1)

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