How to Find the Area of a Circle? Inside 4 Circles
Geometry math problem
Figure shows 4 circles with a radius of 10 cm. The blue circle is tangent to all four circles then find the area of small circle

Solution: Area of the circle
We can connect the center and form a triangle as shown in the figure, where circles are tangential so the angle BAC is tangential (∠BAC = 90°)

From the figure
AB = 20 cm, AC = 20 cm, BQ = 10 cm and PC = 10 cm
Let PQ = 2r = Diameter of the blue circle
To find the area of the circle we need to find the radius of the circle

Apply Pythagoras theorem in triangle ABC
BD² = AB² + AD²
BD² = 20² + 20² = 2×20²
BD = 20 √2
From the figure, we can also get
PQ = BC – 20
PQ = 20√2 – 20 = 20(√2 – 1) cm
So the radius of small circle = 10√2 – 10 cm
Area of the circle = π(10√2 – 10)² = π(200 – 200√2 + 100) = 300π – 200π√2 cm²