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When do you use angle addition postulate and when do you use definition of supplementary angles in geometry?

Imagine a diagram possible like this "___/___" one side is labeled "angle 1" and the other is "angle 2." This is the only information they give me. I would put "measure of angle 1 plus measure of angle 2 equals 180" by angle addition postulate right? If not, explain why. Explain when to use definiton of supplementary angles too please.

This is not the angle addition postulate. The angle addition postulate states that if you have two adjacent angles, you can rename the two small angles as one bigger angle. If the angles are ABC and CBD, where they share ray BC, you can rename these two angles as the large angle ABD. Angle addition postulate would be your reason for saying that ABC + CBD = ABD.

The property your looking for where showing that angle 1 + angle 2 = 180 degrees would either be the definition of a linear pair. Usually we only use definition of supplementary if you have "angle 1 and angle 2 are supplements" as given information. All you showed me as a given is the drawing, which means you can assume a linear pair.

This entry was posted on Saturday, September 12th, 2009 at 8:10 pm and is filed under addition. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

2 Responses to “When do you use angle addition postulate and when do you use definition of supplementary angles in geometry?”

  1. care Says:
    September 13th, 2009 at 1:19 am

    you can use either supplementary or angle addition post. in this example. angle add. can be used for any size angles & any amount of angles but supplementary is only if it equals 180. in this you can use either
    References :

  2. cubs_woo_cubs_woo Says:
    September 13th, 2009 at 2:00 am

    This is not the angle addition postulate. The angle addition postulate states that if you have two adjacent angles, you can rename the two small angles as one bigger angle. If the angles are ABC and CBD, where they share ray BC, you can rename these two angles as the large angle ABD. Angle addition postulate would be your reason for saying that ABC + CBD = ABD.

    The property your looking for where showing that angle 1 + angle 2 = 180 degrees would either be the definition of a linear pair. Usually we only use definition of supplementary if you have "angle 1 and angle 2 are supplements" as given information. All you showed me as a given is the drawing, which means you can assume a linear pair.
    References :
    I’m a high school geometry teacher

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