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
(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