There are five basic types of angles, based on angle measurements. These measurements center around a right, or 90º angle. 90º angles look like an L; they form a perfect corner, like the corner on a piece of paper.

• Acute Angle: an angle that measures less than 90º (think of “a cute little angle”)
• Right Angle: an angle that measures exactly 90º
• Obtuse Angle: an angle that measures more than 90º
• Straight Angle : an angle that measures exactly 180º (a straight line)
• Reflex Angle: an angle that measures more than 180º

There are two pairs of angles that have special properties:

• Complementary Angles: angles that add up to 90º
• Supplementary Angles: angles that add up to 180º

In the example, angles 1 & 2 are complementary, and angles 3 & 4 are supplementary.

When angles are drawn by crossing lines we also create vertical angles.

Vertical Angles: angles that share the same vertex and are created by the same lines.

In the example, angles 2 & 3 are vertical because they have the same vertex and the same lines.

Another type of angle are adjacent angles.

Adjacent Angles: angles right next to each other, sharing a ray between them.

In the example, angles 1 & 2, and 3 & 4 are adjacent.