# Chapter 9: Circles

**Basic**Created by: CK-12

## Introduction

First, we will define all the parts of circles and explore the properties of tangent lines, arcs, inscribed angles, and chords. Next, we will learn about angles and segments that are formed by chords, tangents and secants. Lastly, we will place circles in the coordinate plane and find the equation of and graph circles.

- 9.1.
## Parts of Circles

- 9.2.
## Tangent Lines

- 9.3.
## Arcs in Circles

- 9.4.
## Chords in Circles

- 9.5.
## Inscribed Angles in Circles

- 9.6.
## Inscribed Quadrilaterals in Circles

- 9.7.
## Angles On and Inside a Circle

- 9.8.
## Angles Outside a Circle

- 9.9.
## Segments from Chords

- 9.10.
## Segments from Secants

- 9.11.
## Segments from Secants and Tangents

- 9.12.
## Circles in the Coordinate Plane

### Chapter Summary

## Summary

This chapter begins with vocabulary associated with the parts of circles. It then branches into theorems about tangent lines; properties of arcs and central angles; and theorems about chords and how to apply them. Inscribed angles and inscribed quadrilaterals and their properties are explored. Angles on, inside, and outside a circle are presented in detail and the subsequent relationships are used in problem solving. Relationships among chords, secants, and tangents are discovered and applied. The chapter ends with the connection between algebra and geometry as the equations of circles are discussed.

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