# Geometry: How To Quickly Understand Basic Angles

The basic angles are easy to learn and you’ll have no trouble understanding them. In this lesson you’ll learn about angles and how we can describe different kinds of angles.

## Right Angles

Here are two straight lines meeting at a point.

We call this a **Right Angle** because a square would fit exactly into the corner without leaving any gaps.

The walls of a room are built at right-angles to the floor.

A page of a book usually has a right angle in each corner.

The plus sign: **+ ** shows four right angles.

A small square is often placed in the corner of an angle to show that it’s a right angle. Like this:

## Perpendicular

Another way of saying that two lines are at right-angles to each other is to say that they are perpendicular.

For example: the wall is **perpendicular** to the floor.

## How Four Basic Angles Make a Complete Turn

The minute hand of a clock makes a complete turn in one hour. So in a quarter of an hour it completes a quarter of a turn, and this is the same as a turn of one right angle.

**There are therefore four right angles in a complete turn.**

An angle measures the amount of turn.

## Acute Angles

An angle smaller than a right angle is called an acute angle.

## Obtuse Angles

An angle between 1 and 2 right angles is called obtuse.

## Reflex Angles

An angle between 2 and 4 right angles is called a reflex angle.

For example, both these angles are reflex:

## Now You Try!

You can practice basic angles easily. Simply open your eyes and you’ll discover the wonderful world of angles everywhere.

For example, you’ll find many right-angles in your house, school, workplace and just about everywhere.

You can also discover many places of interest whenever you go out walking. Check out the buildings you see around you and observe how many right angles you spot. Open your eyes to the wonderful world of angles!