In a triangle ABC if a,b,c be length of sides AB,BC,AC then then radius of incircle is given by \[\frac{ \Delta }{s}\]
where \[ \Delta \] is area of the circle which can be evaluated using the formula \[ \sqrt{s(s-a)(s-b)(s-c)}\]
where s is the semi-perimeter of the triangle having length of sides as a ,b,c corresponding to the sides AB,BC,AC respectively.
\[s=\frac{a+b+c}{2}\]
