The degrees of these two angles are equal to 90 degrees.

Equal to 90 degrees

the second type

These angles are all less than 90 degrees.

An angle less than 90 degrees is called an acute angle.

The third category

The degree of the angle is between 90 degrees and 180 degrees.

Angles greater than 90 degrees and less than 180 degrees are called obtuse angles and right angles.

The degrees of this angle are all equal to 180 degrees.

The fourth category: an angle equal to 180 degrees is called a straight angle.