# Geometry

We are surrounded by space. And that space contains lots of things. And these things have shapes. In geometry we are concerned with the nature of these shapes, how we define them, and what they teach us about the world at large--from math to architecture to biology to astronomy (and everything in between). Learning geometry is about more than just taking your medicine ("It's good for you!"), it's at the core of everything that exists--including you. Having said all that, some of the specific topics we'll cover include angles, intersecting lines, right triangles, perimeter, area, volume, circles, triangles, quadrilaterals, analytic geometry, and geometric constructions. Wow. That's a lot. To summarize: it's difficult to imagine any area of math that is more widely used than geometry.
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# Similarity

Learn what it means for two figures to be similar, and how to determine whether two figures are similar or not. Use this concept to prove geometric theorems and solve some problems with polygons.
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All content in “Similarity”

## Definitions of similarity

In this tutorial, you will learn how we determine whether two figures are similar.

## Introduction to triangle similarity

In this tutorial, we will use what we learned about similarity of polygons in the specific case of triangles. We will come up with specific conditions for triangles to be similar, and use them to determine whether two triangles are similar.

## Solving similar triangles

Learn how to find missing measures of triangles using the fact that they are similar to other triangles.

## Angle bisector theorem

Learn about the angle bisector theorem, which makes a clever use of triangle similarity in order to find a special proportion that holds for angle bisectors of triangles.

## Solving problems with similar and congruent triangles

You already saw how we can use similarity and congruence to find missing measures in triangles. Let's do the same now to solve more kinds of polygons, and more challenging problems!

## Solving modeling problems with similar and congruent triangles

Now that you are an expert with solving geometry problems using congruence and similarity, you are ready to solve some real-world problems!