Question:
Four equal circles, each of radius a, touch each other. Show that the area between them is $\frac{6}{7} a^{2}($ Take $\pi=22 / 7)$.
Solution:
It is given that four equal circles of radius a touches each other.
So, Area of circle $=\pi a^{2}$
Since circles touches each other, the lines joining their centre make a square ABCD.
The side of square is 2a.
Area of quadrant inside square $=\frac{1}{4} \pi a^{2}$
Area of shaded region $=$ Area of square $-4 \times$ Area of quadrant
$=(2 a)^{2}-4 \times \frac{\pi a^{2}}{4}$
$=4 a^{2}-\frac{22}{7} a^{2}$
$=\frac{6}{7} a^{2}$