Q.

Three identical circles, each of radius x, are drawn as shown in figure and tangent to a semicircle of radius a, then x in terms of a

1 a4  
2 a2  
3 a3  
4 2a3  

Ans.

(3)

From the diagram, ∠AOB=∠BOC=∠COD=60°⇒∠YOD=π6

Let X be the centre of right-hand circle,  OX sin30°=a

Now r=OY=2a+a=a=r3