Resolution Technique 4 = $ frac {a} {b + c} + frac {b} {a + c} + frac {c} {a + b} $

The question:

4 = $ frac {a} {b + c} + frac {b} {a + c} + frac {c} {a + b} $

Where should I find the minimum values ​​for a, b and c and that they should be positive and complete?

I'm a little confused by all the requests, so it's a bit difficult to understand the quirks. A step in the right direction would be great.