### Angles and Triangles

Geometry involves the understanding of geometric language. When you're studying geometry it's important to learn the properties of figures. This gallery classifies angles and types of triangles and lists the key properties of each figure, along with illustrations.

### Acute Angle

An acute angle measures less than 90 degrees.

### Obtuse Angle

An obtuse angle measures greater than 90 degrees but less than 180 degrees.

### Reflex Angle

A reflex angle measures between 180 and 360 degrees.

### Right Angle

A right angle measures exactly 90 degrees. (Remembering the uppercase letter L will help you remember the angle of a right angle)

### Straight Angle

Straight angles measure exactly 180 degrees.

### Acute Triangle

All angles are acute in an acute triangle.

### Equilateral

Equilateral triangles have three equal sides.

### Isosceles Triangle

Isosceles triangles have two sides that are equal in length.

### Obtuse Triangle

Obtuse triangles have one angle that is obtuse.

### Right Triangle

Right triangles have one right angle.

### Scalene Triangle

Scalene triangles have 3 sides that are all different lengths.

Edited by Anne Marie Helmenstine, Ph.D.