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# The radius of the circle whose arc of length 15 π cm

Question:

The radius of the circle whose arc of length 15 π cm makes an angle of 3π4">3π43π4 radian at the centre is

(a) 10 cm

(b) 20 cm

(c) $11 \frac{1}{4} \mathrm{~cm}$

(d) $22 \frac{1}{2} \mathrm{~cm}$

Solution:

(b) 20 cm

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

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

$\Rightarrow$ Radius $=\frac{60}{3}=20 \mathrm{~cm}$