Jambmaths question:
An arc of a circle subtends an angle of 30oon the circumference of radius 21cm. Find the length of the arc. [take $\pi =\tfrac{22}{7}$]
Option A:
11cm
Option B:
22cm
Option C:
33cm
Option D:
44cm
Jamb Maths Solution:
$\begin{align} & \angle AOB=\angle ACB\text{ }\{angle\text{ }at\text{ }centre=2\times angle\text{ }at\text{ }circum\} \\ & \angle AOB=2\times {{30}^{\text{o}}}={{60}^{\text{o}}} \\ & \text{Length of arc }ACB=\frac{\theta }{360}\times 2\pi r \\ & =\frac{60}{{{360}^{\text{o}}}}\times 2\times \frac{22}{7}\times 21cm \\ & =22cm \\\end{align}$
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