# What is a right angle, acute angle, and obtuse angle?

##### 1 Answer

*Right* angle is half of *straight* angle.

*Acute* angle has a smaller measure than *right* one, while *obtuse* angle has a bigger measure than *right* one.

See below for details.

#### Explanation:

We should start with a concept of an *angle*.

An *angle* is a geometric object formed by two *half-lines* (*rays*) with a common endpoint called *vertex*.

Strictly speaking, there are two angles formed this way: from Ray1 to Ray2 clockwise and counterclockwise.

If Ray1 and Ray2 coincide, the angle between them is called *full* since it takes a full circle to move Ray1 to Ray2.

The measure of a *full* angle is, by definition, equal to

Obviously, angles measured at

In this terminology, if Ray1 and Ray2 are located along the same line but directed opposite to each other, they form half of a *full* angle, this angle is called *straight* and is measured at

Half of a *straight* angle would be formed by perpendicular to each other Ray1 and Ray2. This is the *right* angle, and its measure in degrees is

*Acute* angles are smaller than *right* ones and *obtuse* angles are bigger.