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# Complementary and supplementary angles review

Review the basics of complementary and supplementary angles, and try some practice problems.

## Complementary angles

Complementary angles are two angles with a sum of 90, degrees. A common case is when they form a right angle.

## Supplementary angles

Supplementary angles are two angles with a sum of 180, degrees. A common case is when they lie on the same side of a straight line.

## Practice set 1: Identify complementary and supplementary angles

Problem 1A
• Current
What is the relationship between angle, A, X, Y and angle, Y, X, B?
All segments that appear straight are straight.

Want to try more problems like this? Check out this exercise.

## Practice set 2: Find a missing angle measure

Problem 2A
• Current
If angle, A, O, C is a right angle and m, angle, A, O, B, equals, 79, degrees, what is m, angle, B, O, C?
Note: Angles not necessarily drawn to scale.
degrees

Want to try more problems like this? Check out this exercise.

## Want to join the conversation?

• I'm confused with complementary angles and supplementary angles. How do you tell which angle is which?
• Two angles are called complementary when their measures add to 90 degrees.
Two angles are called supplementary when their measures add up to 180 degrees.

One way to avoid mixing up these definitions is to note that s comes after c in the alphabet, and 180 is greater than 90.
• How do they come up with names for things in math?
• probably latin
• About question 1, I hope there is a clear explanation on why ∠DAP and ∠BPD do not add up to 90°. I guess there is some reason why ∠DAP and ∠BPD being supplementary or complementray is a contradiction, but i couldn't figure out what it is.
• They might be complementary or supplementary, but you don't have enough information to prove that. There are no parallel lines, so you can't try and solve it using any of the parallel lies and a transversal rules. No vertical angles will end up helping you. I guess you can't really have a clear answer, unless you can prove that the angles cannot be complementary or supplementary.
• One tip that helps me with remembering which name goes with which angles...

- "C" is in 'Corner' and 'Complementary'
- "S" is in 'Straight' and 'Supplementary'

A corner is always 90 degrees...
and a straight line is always 180 degrees!

So if it makes a corner, it's 'C' for 'Complementary'
if it makes a straight line, it's 'S' for 'Supplementary'
• What are vertical angles? I am asking this because I have some trouble identifying this certain type of angle.
(1 vote)
• say angle A is on one side of the vertex and angle B is on the opposite side, since they share a vertex and are on the opposite side of said vertex, they are vertical
• I need help with practice step 2. Thank you.
• What exactly are you confused about? If you can be more specific with what you need assistance for I will be glad to walk you through it :)
• What do they mean with "A common case is when they form a right angle." and "A common case is when they lie on the same side of a straight line." ?

Aren't those the ONLY cases for complementary and supplementary angles?
• No these are not the only cases. For example, the two acute angles of a right triangle are complementary. Another example: if two parallel lines are cut by a transversal, then any pair of same side interior angles is supplementary.

Have a blessed, wonderful day!
(1 vote)
• URGENT! Is there a video about understanding angle relationships with the intersection lines?