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Mathematics — Standard (041) — CBSE Class 10 board question

Q1. [1] § 8.5 Summary
For an acute angle $\theta$, if $\sin\theta = \frac{1}{9}$, then value of $\frac{9\csc\theta + 1}{9\csc\theta - 1}$ is
  1. (A) $0$
  2. (B) $\frac{80}{81}$
  3. (C) $1$
  4. (D) $\frac{82}{80}$
Previously asked in CBSE board exam
2026 30/5/1 Q14
Generated by claude-sonnet-4-6 · 2026-06-15 10:27 · grounding rag
Model Answer

Since $\sin\theta = \dfrac{1}{9}$, we have $\csc\theta = \dfrac{1}{\sin\theta} = 9$.

$$\frac{9\csc\theta + 1}{9\csc\theta - 1} = \frac{9(9) + 1}{9(9) - 1} = \frac{81 + 1}{81 - 1} = \frac{82}{80}$$

Answer: (D) $\dfrac{82}{80}$

Source: Chapter 8, Section 8.2 (Trigonometric Ratios)

Explanation

The key step is recognising that $\csc\theta = \dfrac{1}{\sin\theta} = \dfrac{1}{1/9} = 9$. Substituting directly gives the value. Examiners expect students to recall the reciprocal relation $\csc\theta = \dfrac{1}{\sin\theta}$ instantly and substitute without complicated working.

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