AoPSWiki

Our Precalculus course starts on Dec. 4. Master trig, complex numbers, and vectors and matrices in 2 and 3 dimensions. Click here to enroll today!

Personal tools

Log in

Search

Toolbox

Inradius

From AoPSWiki

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

Properties

If $\triangle ABC$ has inradius $r$ and circumradius $R$ , then $\cos{A}+\cos{B}+\cos{C}=\frac{r+R}{R}$ .

Retrieved from "http://www.artofproblemsolving.com/Wiki/index.php/Inradius"

Category: Geometry

Want to learn how to tackle those tough AMC/AIME/Olympiad algebra problems? Check out Art of Problem Solving's Intermediate Algebra by Richard Rusczyk and Mathew Crawford. Over 1600 problems!

© Copyright 2008 AoPS Incorporated. All Rights Reserved. • Foundation • Privacy • Contact Us