Need to prove:

Right hand side

, where s is half of perimeter of triangle.

4(s(s – a) + s(s – b) + s(s – c))

4(3s² – s(a + b + c))

We know, 2s = a +b +c

So,

3(a + b + c)² – 2(a + b + c)²

(a + b + c)²

Right hand side. [Proved]