If $\sec x+\tan x=3, x \in\left(0, \frac{\pi}{2}\right)$ then, $\sin x=$

If $\sec x+\tan x=3, x \in\left(0, \frac{\pi}{2}\right)$ then, $\sin x=$
  1. $\frac{3}{5}$
  2. $\frac{4}{5}$
  3. $-1$
  4. $\frac{1}{5}$

Solution

We have $\sec x+\tan x=3$ ...(1) We know that $\sec ^{2} x-\tan ^{2} x=1$ $\therefore(\sec x-\tan x)(\sec x+\tan x)=1 \Rightarrow \sec x-\tan x=\frac{1}{3}$ ...(2) Adding (1) and (2) $2 \sec x=\frac{10}{3} \Rightarrow \sec x=\frac{5}{3} \Rightarrow \cos x=\frac{3}{5} \Rightarrow \sin x=\sqrt{1-\cos ^{2} x}=\frac{4}{5}$

Asked in: MHT CET 2020 (12 Oct Shift 1)

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