Question

The radius of the circle whose arc of length $15\pi$cm makes an angle of $\frac{3\pi }{4}$ radian at the centre is

• A. 10 cm
• B. 20 cm
• C. $11\frac{1}{4}cm$
• D. $22\frac{1}{2}cm$

Answer 1

The correct option is B

20 cm

$\theta =\frac{\text{Arc}}{\text{Radius}}$

$\Rightarrow \frac{3\pi }{4}=\frac{15\pi }{\text{Radius}}\Rightarrow$ Radius $=\frac{60}{3}$

= 20 cm