Problem 7
The fan is symmetric and circles O1, O2 and O3 lie between two cocentric circles with centre O as shown.
O1, O2 and O3 have radii r1, r2 and r3 respectivly and touch each other externally as shown.
Also O2 and O3 touch line AO at points B and C.
Let the length of AO = a
Find r2 in terms of a and r1.
