1. Geometry is about shapes and their properties

2. Acute angle is always less than 90°

3. Obtuse angle is larger than 90° and smaller than 180°

4. Right angle is an internal angle equal to 90° Note the special symbol like a box in the angle. If you see this, it is a right angle. The 90° is rarely written in. If you see the box in the corner, you are being told it is a right angle.

5. Straight angle measure 180° A straight angle changes the direction to point the opposite way. Sometimes people say "You did a complete 180° on that!"... meaning you completely changed your mind, idea or direction.