An Introduction to Angles

Introduction to Angles

Introduction to Angles

Welcome to this video lesson about acute and obtuse angles.

When first learning geometry, you’ll need to know the basics, and there’s no better place to start than with angles.

1st, Right angles are vital to everything in geometry. A right angle is 90 degrees. You find them in triangles, squares, rectangles, where walls meet floors, houses, windows, everything. Just remember 90 degrees is a right angle… it’s like the perfect corner.

2nd, Now, for acute angles, these are angles that are less than 90 degrees. These are very common as well, but there is less information associated with them. When a problem says you start with a Right angle, you immediately know it’s 90 degrees. If they say you start with an acute angle, it means anything between 0 and 90, so it can be trickier.

3rd, Obtuse angles. These are angles that are more than 90 degrees but less than 180 degrees (which is a straight line). That means an angle that is not a straight line, but not a Right angle, yet somewhere in between. These are also common everywhere around us, and especially in geometry.

So, let’s run through some examples of what this looks like.

Here’s an angle. At first glance is it acute, right, or obtuse?


We know this because it’s smaller than a right angle.

Here’s another: An angle is 108 degrees… What is it?


Here’s another, what is this?

It’s likely a right angle at 90 degrees.

Here are two acute angles, if added together, will they be acute, right, or obtuse?


Here’s an obtuse angle, if you subtract 38 degrees, what will it be?

It will be a right angle.

I hope that helps. Thanks for watching this video lesson, until next time, happy studying.



by Mometrix Test Preparation | Last Updated: March 26, 2019