<Dd> T = r a (s − a) = r b (s − b) = r c (s − c) (\ displaystyle T = r_ (a) (s-a) = r_ (b) (s-b) = r_ (c) (s-c)) </Dd> <P> where r a, r b, r c (\ displaystyle r_ (a), \, r_ (b), \, r_ (c)) are the radii of the excircles tangent to sides a, b, c respectively . </P> <P> We also have </P> <Dl> <Dd> T = 1 2 D 2 (sin ⁡ α) (sin ⁡ β) (sin ⁡ γ) (\ displaystyle T = (\ frac (1) (2)) D ^ (2) (\ sin \ alpha) (\ sin \ beta) (\ sin \ gamma)) </Dd> </Dl>

What is the condition to make a triangle