Difference between revisions of "Inradius"

Revision as of 14:54, 14 March 2010

The inradius of a polygon is the radius of its incircle (assuming an incircle exists). It is commonly denoted $r$ .

If $\triangle ABC$ has inradius $r$ and circumradius $R$ , then $\cos{A}+\cos{B}+\cos{C}=\frac{r+R}{R}$ .
If $\triangle ABC$ has inradius $r$ and semi-perimeter $s$ , then the area of $\triangle ABC$ is $rs$ .

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 == Properties ==
 *If <math>\triangle ABC</math> has inradius <math>r</math> and [[circumradius]] <math>R</math>, then <math>\cos{A}+\cos{B}+\cos{C}=\frac{r+R}{R}</math>.
-*If <math>\triangle ABC</math> has inradius <math>r</math> and [[semi-perimeter]] <math>s</math>, then the [[area]] of <math>ABC</math> is <math>rs</math>.
+*If <math>\triangle ABC</math> has inradius <math>r</math> and [[semi-perimeter]] <math>s</math>, then the [[area]] of <math>\triangle ABC</math> is <math>rs</math>.
 [[Category:Geometry]]