Question : Two identical circles each of radius $2\;\mathrm{cm}$ intersect each other such that the circumference of each one passes through the centre of the other. What is the area (in $\mathrm{cm^2}$) of the intersecting region?
Option 1: $\frac{8\pi }{3}-2\sqrt{3}$
Option 2: $\frac{8\pi }{3}-\sqrt{3}$
Option 3: $\frac{4\pi }{3}-\sqrt{3}$
Option 4: $\frac{4\pi }{3}-2\sqrt{3}$
Correct Answer: $\frac{8\pi }{3}-2\sqrt{3}$
Solution : Given that the area of the intersecting region of two identical circles each of radius $2\;\mathrm{cm}$. In triangle $\mathrm{AOO', OA = O'A = OO'} = 2\;\mathrm{cm}$ It is an equilateral triangle. $\angle \mathrm{AOO'} = 60^\circ$ $\angle \mathrm{AOB} = 120^\circ$ In $\triangle \mathrm{ACO}$, $\mathrm{AC^2 = OA^2 - OC^2} = 4 - 1 = 3$ $\mathrm{AC} = \sqrt{3}$ $\mathrm{AB} = 2\sqrt{3}$ Area of $\mathrm{AO'BA} =$ Area of sector $\mathrm{AO'BO} $$-$ Area of triangle $\mathrm{AOB}$ $=2\times\frac{60^\circ\pi(2)^2}{360^\circ} - \frac{1}{2} \times 2\sqrt{3} \times 1$ $=\frac{\pi (2)^2}{3} - \frac{1}{2} \times 2\sqrt{3} \times 1$ $=\frac{4\pi}{3} - \sqrt{3}$ Area of intersecting region $= 2$ (Area of $\mathrm{AO'BA}$) $=2 \left(\frac{4\pi}{3} - \sqrt{3}\right) =\left(\frac{8\pi}{3} - 2\sqrt{3}\right)\;\mathrm{cm^2}$ Hence, the correct answer is $\frac{8\pi }{3}-2\sqrt{3}$.
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