Q1. [1] § Introduction to Trigonometry (Chapter Header and Quote) § 8.5 Summary
If $\theta$ is an acute angle and $7 + 4\sin\theta = 9$, then the value of $\theta$ is:
- A $90°$
- B $30°$
- C $45°$
- D $60°$
Previously asked in CBSE board exam
2025 30/1/1 Q4
Generated by claude-sonnet-4-6 · 2026-06-15 10:21 · grounding rag
Model Answer
Option (B) 30°
$7 + 4\sin\theta = 9 \Rightarrow 4\sin\theta = 2 \Rightarrow \sin\theta = \dfrac{1}{2}$. Since $\sin 30° = \dfrac{1}{2}$, therefore $\theta = 30°$.
Explanation
Solve the equation to find $\sin\theta = \frac{1}{2}$, then use the standard values table (Table 8.1) from Chapter 8. Remember $\sin 30° = \frac{1}{2}$ is a must-memorise value. Always show the algebraic step before stating the angle.
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