# 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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# Angles & intersecting lines

This topic continues our journey through the world of Euclid by helping us understand angles and how they can relate to each other.
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All content in “Angles & intersecting lines”

## Angle basics & measurement

This tutorial will define what an angle is and help us think about how to measure them. If you're new to angles, this is a great place to start.

## Angle types

Explore the different types of angles

## Complementary & supplementary angles

In this tutorial we'll look at the most famous types of angle-pairs--complementary and supplementary angles. This aren't particularly deep concepts, but you'll find they do come in handy!

## Angles between intersecting and parallel lines

Welcome. I'd like to introduce you to Mr. Angle. Nice to meet you. So nice to meet you. This tutorial introduces us to angles. It includes how we measure them, how angles relate to each other and properties of angles created from various types of intersecting lines. Mr. Angle is actually far more fun than you might initially presume him to be.

## Angles with triangles & polygons

Do the angles in a triangle always add up to the same thing? Would I ask it if they didn't? What do we know about the angles of a triangle if two of the sides are congruent (an isosceles triangle) or all three are congruent (an equilateral)? This tutorial is the place to find out.

## Angles with polygons

Explore properties of angles in and arou polygons.

## Sal's old angle videos

These are some of the classic, original angle video that Sal had done way back when (like 2007). Other tutorials are more polished than this one, but this one has charm. Also not bad if you're looking for more examples of angles between intersected lines, transversals and parallel lines.