This is not true in general because if it were true in general it would hold true for an equilateral triangle with a = b = c = 1 and A = B = C = 60° Substituting:Which is false. So since it is false for an equilateral triangle with all sides 1 and all angles 60°, it is NOT true in general. If you inadvertently typed it incorrectly, you may tell me in the form below and I'll get back to you by email. There is never any charge as I am a retired mathematics teacher and I do this for fun. Edwin