If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Lesson 1: Decomposing angles

# Decomposing an angle

Sal finds the measure of angles by adding or subtracting. Created by Sal Khan.

## Want to join the conversation?

• how can we measure angles of hands of a clock without using a protractor its not given in the syllabus, help me.
• You actually can do it without a protractor. There are 12 numbers on a clock. So the distance between each number is 30 degrees. You can use that to measure the angles.
• how can you tell if its a obtuse angle or a right angle
• An obtuse angle is an angle greater than 90 degrees but less that 180. A right angle, on the other hand, is an angle EXACTLY 90 DEGREES OF MEASURE. Usually, a right angle is marked by a square inside of the angle. Also usually, a geometric problem says "Not drawn to scale" so you can't assume it's 90 degrees.

(Sorry, I'm 5 yrs late)
• Can you decompose more than one angle?
• Yes we can classify more than one angle
• is there another way to get the angle
• You can use the trigonometric ratios, but the best way is to use a protractor to measure it. If you really want to know all the ways to calculate an angle, you can go to the trigonometry subject. Good luck
• Does decomposing mean breaking angles equally? please give me full description. Thanks for answering!
• Hi! Decomposing an angle is when you subtract the interior angle's number of degrees (not really sure how to word it...) from the outer angle's number of degrees. I'll explain the problem Sal does in this video.

It's asking 'what is the measure of angle COB?' This means you have to find out how many degrees angle COB is.

It shows you that the angle between D and B is 70°. It also shows that the angle between D and C is 45.

You would want to subtract the full 70° between D and B minus the interior 45° between D and C to get the angle of COB.

Therefore, COB equals:

70° - 45° = COB -----> Angle COB equals 25°.

Hope this helped! :)
• Something that is near by, in this case the angle which is near to the other. so the 45 degree angle is adjacent to the 25 degree angle and their sum is going to be 70 degree.
• ⢀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⠀⠀⠀
⢠⣾⡿⠿⠛⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⠀
⢸⣿⢠⠞⣩⡄⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠿⠛⠉⠉⠀⠀⠀⠀⠉⠛⢿⡆
⢸⣿⣄⣈⣉⣴⣿⣿⣿⣿⣿⣿⣿⠟⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⠟⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⡿⠃⠀⠀⠀⠀⠀⠀⣀⣀⣀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⡟⠁⠀⠀⢀⣤⣶⣿⣿⣿⣿⣿⣿⣿⣷⣤⡀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⡏⠀⠀⢀⣴⣿⣿⣿⣿⣿⠿⠿⠿⣿⣿⣿⣿⣷⡄⠀⠀⠀⠀⠀⠀
⢸⣿⠏⠀⠀⢠⣿⣿⣿⣿⠟⠁⠀⠀⣠⣶⣿⣿⣿⣿⣿⣿⠀⠀⠀⠀⠀⠀
⢸⡟⠀⠀⢠⣿⣿⣿⡟⠁⠀⢀⣠⣾⣿⣿⣿⡿⠋⣿⣿⣿⡇⠀⠀⠀⠀⠀
⠘⠀⠀⠀⢸⣿⣿⣿⠁⢀⣴⣿⣿⢿⣿⠿⠋⠀⢀⣿⣿⣿⠇⠀⠀⠀⣼⠀
⠀⠀⠀⠀⢸⣿⣿⣿⣶⣿⣿⣿⣿⠟⠁⠀⠀⢠⣾⣿⣿⡿⠀⠀⠀⣼⣿⠀
⠀⠀⠀⠀⠀⢿⣿⣿⣿⣿⣿⠟⠁⠀⣀⣠⣶⣿⣿⣿⡿⠁⠀⠀⣼⣿⣿⠀
⠀⠀⠀⠀⠀⠈⢿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⢀⣾⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠙⠻⠿⣿⣿⣿⣿⣿⠿⠟⠋⠀⠀⠀⣠⣾⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣼⣿⣿⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣿⣿⣿⣿⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠀
⢀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣠⣾⣿⣿⣿⣿⣿⣿⣿⠟⣋⠛⢿⣿⠀l
⢸⣷⣤⣀⡀⠀⠀⠀⣀⣠⣤⣶⣿⣿⣿⣿⣿⣿⣿⣿⣿⡇⠞⣡⡼⢸⣿⠀
⠈⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⣤⣥⣴⣿⠟⠀
• S⢀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⠀⠀⠀
⢠⣾⡿⠿⠛⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⠀
⢸⣿⢠⠞⣩⡄⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠿⠛⠉⠉⠀⠀⠀⠀⠉⠛⢿⡆
⢸⣿⣄⣈⣉⣴⣿⣿⣿⣿⣿⣿⣿⠟⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⠟⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⡿⠃⠀⠀⠀⠀⠀⠀⣀⣀⣀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⡟⠁⠀⠀⢀⣤⣶⣿⣿⣿⣿⣿⣿⣿⣷⣤⡀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⡏⠀⠀⢀⣴⣿⣿⣿⣿⣿⠿⠿⠿⣿⣿⣿⣿⣷⡄⠀⠀⠀⠀⠀⠀
⢸⣿⠏⠀⠀⢠⣿⣿⣿⣿⠟⠁⠀⠀⣠⣶⣿⣿⣿⣿⣿⣿⠀⠀⠀⠀⠀⠀
⢸⡟⠀⠀⢠⣿⣿⣿⡟⠁⠀⢀⣠⣾⣿⣿⣿⡿⠋⣿⣿⣿⡇⠀⠀⠀⠀⠀
⠘⠀⠀⠀⢸⣿⣿⣿⠁⢀⣴⣿⣿⢿⣿⠿⠋⠀⢀⣿⣿⣿⠇⠀⠀⠀⣼⠀
⠀⠀⠀⠀⢸⣿⣿⣿⣶⣿⣿⣿⣿⠟⠁⠀⠀⢠⣾⣿⣿⡿⠀⠀⠀⣼⣿⠀
⠀⠀⠀⠀⠀⢿⣿⣿⣿⣿⣿⠟⠁⠀⣀⣠⣶⣿⣿⣿⡿⠁⠀⠀⣼⣿⣿⠀
⠀⠀⠀⠀⠀⠈⢿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⢀⣾⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠙⠻⠿⣿⣿⣿⣿⣿⠿⠟⠋⠀⠀⠀⣠⣾⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣼⣿⣿⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣿⣿⣿⣿⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠀
⢀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣠⣾⣿⣿⣿⣿⣿⣿⣿⠟⣋⠛⢿⣿⠀
⢸⣷⣤⣀⡀⠀⠀⠀⣀⣠⣤⣶⣿⣿⣿⣿⣿⣿⣿⣿⣿⡇⠞⣡⡼⢸⣿⠀
⠈⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⣤⣥⣴⣿⠟⠀
• it is uno
• Hello. I'm sorry, but is the angles from video are adjacent? Indeed, angles shares vertex and one ray, but other rays need to compose a straight line. Maybe these angles are included? Correct me please if I'm wrong.
• A pair of adjacent angles are angles that, as you said, share a common vertex and one ray, but the incorrect part is that they don't need to create a 180 degree angle (straight line) and they can be considered adjacent as long as they are "next to each other." Good luck!
• S⢀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⣀⠀⠀⠀
⢠⣾⡿⠿⠛⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⠀
⢸⣿⢠⠞⣩⡄⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠿⠛⠉⠉⠀⠀⠀⠀⠉⠛⢿⡆
⢸⣿⣄⣈⣉⣴⣿⣿⣿⣿⣿⣿⣿⠟⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⣿⣿⠟⠁⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⣿⡿⠃⠀⠀⠀⠀⠀⠀⣀⣀⣀⡀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⣿⡟⠁⠀⠀⢀⣤⣶⣿⣿⣿⣿⣿⣿⣿⣷⣤⡀⠀⠀⠀⠀⠀⠀⠀
⢸⣿⣿⡏⠀⠀⢀⣴⣿⣿⣿⣿⣿⠿⠿⠿⣿⣿⣿⣿⣷⡄⠀⠀⠀⠀⠀⠀
⢸⣿⠏⠀⠀⢠⣿⣿⣿⣿⠟⠁⠀⠀⣠⣶⣿⣿⣿⣿⣿⣿⠀⠀⠀⠀⠀⠀
⢸⡟⠀⠀⢠⣿⣿⣿⡟⠁⠀⢀⣠⣾⣿⣿⣿⡿⠋⣿⣿⣿⡇⠀⠀⠀⠀⠀
⠘⠀⠀⠀⢸⣿⣿⣿⠁⢀⣴⣿⣿⢿⣿⠿⠋⠀⢀⣿⣿⣿⠇⠀⠀⠀⣼⠀
⠀⠀⠀⠀⢸⣿⣿⣿⣶⣿⣿⣿⣿⠟⠁⠀⠀⢠⣾⣿⣿⡿⠀⠀⠀⣼⣿⠀
⠀⠀⠀⠀⠀⢿⣿⣿⣿⣿⣿⠟⠁⠀⣀⣠⣶⣿⣿⣿⡿⠁⠀⠀⣼⣿⣿⠀
⠀⠀⠀⠀⠀⠈⢿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⡿⠋⠀⠀⢀⣾⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠙⠻⠿⣿⣿⣿⣿⣿⠿⠟⠋⠀⠀⠀⣠⣾⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣼⣿⣿⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣿⣿⣿⣿⣿⣿⣿⣿⠀
⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣴⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⠀
⢀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⣠⣾⣿⣿⣿⣿⣿⣿⣿⠟⣋⠛⢿⣿⠀
⢸⣷⣤⣀⡀⠀⠀⠀⣀⣠⣤⣶⣿⣿⣿⣿⣿⣿⣿⣿⣿⡇⠞⣡⡼⢸⣿⠀
⠈⠿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣿⣷⣤⣥⣴⣿⠟⠀