If $\operatorname{cosec} \theta+\cot \theta=5$, then $\sin \theta=$

If $\operatorname{cosec} \theta+\cot \theta=5$, then $\sin \theta=$
  1. $\frac{1}{5}$
  2. $\frac{5}{26}$
  3. $\frac{5}{13}$
  4. $\frac{1}{13}$

Solution

Given $\operatorname{cosec} \theta+\cot \theta=5$ We know that $\operatorname{cosec}^{2} \theta-\cot ^{2} \theta=1$ $\Rightarrow(\operatorname{cosec} \theta-\cot \theta)(\operatorname{cosec} \theta+\cot \theta)=1 \Rightarrow \operatorname{cosec} \theta-\cot \theta=\frac{1}{5}$ Adding (1) \& (2), we get $2 \operatorname{cosec} \theta=5+\frac{1}{5}=\frac{26}{5}$ $\therefore \operatorname{cosec} \theta=\frac{13}{5} \Rightarrow \sin \theta=\frac{5}{13}$

Asked in: MHT CET 2020 (14 Oct Shift 1)

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