# Radii of in-circle and ex-circles of a right- angled triangle

Miraj, Rahil (2019) Radii of in-circle and ex-circles of a right- angled triangle. At Right Angles (4). pp. 27-30. Text - Published Version Download (171kB)

## Abstract

In this article, I provide a relation connecting the lengths of the tangents from the vertices of a right-angled triangle to its incircle and ex-circles, in terms of its inradius and ex-radii. I give a geometric proof as well as an analytic proof. A standard result which will be used repeatedly is the following: Given a circle and a point outside it, the lengths of the two tangents that can be drawn from the point to the circle have equal length. A list of more such results and formulas of relevance is provided at the end of the article. The following nomenclature should be noted. Other than the incircle of a triangle, three other circles can be drawn that touch the sidelines of a triangle. These are called the ex-circles of the triangle. The ex-circle opposite vertex A is known as the ‘A ex-circle’, and likewise for the two other ex-circles. The radius ra of the A ex-circle is called the ‘A ex-radius’, and similarly for the radii of the two other ex-circles.

Item Type: Articles in APF Magazines Incircle, Ex-circle, Tangent, Pythagorean triangle, Pythagorean triple Natural Sciences > Mathematics Azim Premji University > University publications > At Right Angles Mr. Sachin Tirlapur 25 Jul 2019 10:32 26 Jul 2019 11:10 http://publications.azimpremjifoundation.org/id/eprint/2023 View Item