Find the length of an arc of a circle of radius $21\text{ cm}$ which subtends an angle of $60^\circ$ at the centre.
Step-by-Step Solution
Key Concept: $l = \dfrac{\theta}{360^\circ} \times 2 \pi r = \dfrac{60}{360} \times 2 \times \dfrac{22}{7} \times 21 = \dfrac{1}{6} \times 132 = 22\text{ cm}$.
$l = \dfrac{60}{360} \times 2 \times \dfrac{22}{7} \times 21 = \dfrac{1}{6} \times 132$. [1.0 Mark]
$l = 22\text{ cm}$. [1.0 Mark]
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🎯 Official CBSE Marking Scheme:
Applying arc length formula: 1.0 Mark
Evaluating arc length $= 22\text{ cm}$: 1.0 Mark
Correct Answer: