I'm trying to solve the following problem : 

In $△ABC$, $AB = AC, BC = 48$ and inradius $r = 12$. Find the
circumradius $R$.

Here is a figure that I drew : ( note : it was not given in the question so there may be some mistakes ) 
![Figure](https://i.stack.imgur.com/barvM.png)

I don't know how to solve it , am I missing any relation between inradius , circumradius and sides of a isosceles triangle?

EDIT: Is there a simple solution without using trigonometry ?