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Naming angles

Sal names angles based on their vertex and endpoints. Created by Sal Khan.

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  • piceratops seed style avatar for user 19ericresendiz
    Couldn't we distinguish two angles - one "interior" and another "exterior"?
    (17 votes)
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  • duskpin ultimate style avatar for user ☁︎~cosmickiwi~☁︎
    At , Sal said that you can't name the angle <CPA <PAC, why?
    I know he explained, and probably properly, but I still don't understand! This is frustrating!
    ...
    Sorry for the outburst. :| Someone, please explain!

    This problem has been resolved. Thank you! :)
    (9 votes)
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    • female robot amelia style avatar for user Johanna
      The letter in the middle of the angle’s name has to be the point of the angle’s vertex. We know from the name ∠CPA that point P is the vertex of the angle in question. Since P is the vertex, any other name we could give to that same angle would have to stay true to which point is the angle’s vertex, meaning that P would have to be in the middle of the angle’s name. Another acceptable name for ∠CPA would be ∠APC

      ∠PAC would mean that point A is the angle’s vertex, which would mean that ∠PAC and ∠CPA couldn’t be naming the same angle.

      Does that make sense?
      (12 votes)
  • piceratops sapling style avatar for user Carlos
    How did you get tht answer
    (12 votes)
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  • winston default style avatar for user Meah
    what does m<1 or m<2 mean? (< is a substitution for the angle symbol.)
    (6 votes)
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  • duskpin seed style avatar for user peachyblue
    Hi I am on the updated course and am struggling with NAME ANGLES. If anybody has finished ths course could you please explain? Thanks.
    (7 votes)
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    • piceratops ultimate style avatar for user Carl Chen
      Angles need to be expressed with names just like humans. The way we name them is by using the points given. For example, image an open angle with point A on the first line and point B as the vertex (the point where the two lines intersect to form the angle) and point C on the other side. It's something like this:
      |
      |*A (imagine the dot is on that line)
      |
      | (imagine C is on this line lying down)
      *B _______*C_______
      (imagine B is where they touch each other)

      If you can't visualize it then draw it on paper.
      So the way we would call this angle is Angle ABC because the if you imagine drawing through the angle in one line you would start your line at point A and trace all the way to B, make a turn, and go to point C.

      Do you understand the first part? If not you can ask me again for more explanation :D

      Ok now for the second way. We can name an angle simply by saying *angle [B]* (B is the vertex).This only applies when the vertex *DOES NOT INVOLVE IN OTHER ANGLES!* The graph above would be an example because the vertex B only form that one angle. BUT IN THIS EXAMPLE:
      For example: Imagine two lines crossing each other, and B is the point where they cross.
      the vertex point B forms a lot of angles. Therefore you cannot name the angle with one letter because people won't know which angle you are talking about. In this situation you need to use three letters method.
      (6 votes)
  • starky sapling style avatar for user 28wnguyen
    Is there a practice quiz after this?
    (6 votes)
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  • male robot donald style avatar for user ttv_JustMeDiamond
    When you write CAP or XYZ or whatever, why is it always capital?
    (5 votes)
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    • female robot grace style avatar for user benincm
      When naming an angle or a shape, mathematicians tend to use capital letters, because they aren't expecting you to do math operations with those letters. They are known values and don't need to be calculated. They are like names, as opposed to other kinds of words. If someone were to write your name as "abirbakshi" instead of "AbirBakshi," then someone who didn't know it was your name might think it was a regular word with a defintion (or value) and try to measure or describe you like they would a table or other object. That would be wrong. So, we name things that are known values with capitals to differentiate between them and the small letters that we use to represent unknown values as used in algebra or geometry. It's okay to measure or calculate using "x" or "y" but not "X" or "Y."
      (10 votes)
  • blobby green style avatar for user clayton.turner
    how are some angels different from other angels
    (4 votes)
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  • blobby green style avatar for user 127591
    which type of angel is 180?
    (4 votes)
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  • aqualine seed style avatar for user Daisy Lawlor
    Im finding it difficult is that
    normal?
    (3 votes)
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Video transcript

What is another name for angle CPA? So we have C, we have P, and we have A. So angle CPA is going to be this angle right over here. So what's another name for it? Well, I could start off with A, and I could call it angle APC. So this is the same thing as angle APC. Now is that any one of my choices? Yeah, that's this choice right over here. If someone said angle P, that wouldn't give you a lot of information. That kind of says, well, that's only giving me one point. I don't know, maybe it's referring to that angle, that angle, that angle, that angle. So that's really not giving me enough information to specify this angle right over here. Angle PAC would be an angle formed if you actually had a line here, if you had a line between AC. Angle PAC would be this angle right over here, which is clearly a different angle. Angle FPA would be this angle right over here, which is also clearly a different angle. So the only choice that makes sense is angle APC.