# Geometry Help and Problems

This section is all about key geometric concepts, theorems, and proofs. Learn how to write mathematical arguments in the form of a two-column geometric proof and study the different properties of shapes by working through these insightful lessons.

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## Introduction to Geometry

Just starting out in geometry? This group of lessons will introduce you to the mathematical study of shapes. Geometry is one of the oldest branches of mathematics, with a rich history and many different real world applications. Read on to learn the geometry basics you should know as a beginning student.

## Lines and Angles

Lines and angles are some of the most important topics in geometry. These lessons will teach you about their different properties, as well as the different categories of lines and angles you’ll need to be familiar with as a geometry student. Our section on lines and angles ends with an introduction to postulates and theorems.

## Triangles

Do you know the difference between equilateral and equiangular triangles? Can you prove the congruence of two triangles? The study of these three-sided shapes is the first step after learning about lines and angles, and will provide an essential foundation for future topics in geometry.

## Quadrilaterals

Quadrilaterals are the next topic for advancing geometry students. Unlike triangles, these four- sided polygons come in many different shapes: squares, rectangles, trapezoids, and more. In these lessons, you will learn the properties of different quadrilaterals and expand your knowledge of geometry.

## Areas of Polygons and Circles

Once you’ve become familiar with different shapes, you can start to examine them in more complicated ways. These lessons describe how to calculate the areas of polygons and circles. We also include helpful reference tables you can use for homework or test review.