Classifying Angles
Angles can be classified in many ways, depending on their size. You can name angles just by looking at them. As you can see from the examples above, there are acute, obtuse, right, straight, reflex and revolution angles. Acute angles are less than 90º, while obtuse angles are greater than 90º but smaller than 180º. Right angles are exactly 90º and are marked with a box symbol. Straight angles are 180º, as it is half of 360º, which is a revolution angle. Finally, there is a reflex angle, which is between 180º and 360º.
Below are some useful angle facts:
Below are some useful angle facts:
Angles and parallel lines
When parallel lines are cut with a transversal, they make certain types of angles. These angles are called alternate, corresponding and co-inerior angles. It is very important that you know these angles and what they look like. Alternate angles make a Z shape, and are always equal. When trying to find the unknown angle, this is very useful. Corresponding angles make a F shape, and are also equal. Again, when trying to find the unknown, use corresponding angles if you can. Finally, co-interior angles. Co-interoir angles always add up to 180º, and we call this supplementary (complementary angles add up to 90º).