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What is the justification for the congruent proof that the measure of angle A + the measure of angle B=180?

I'm doing one-step proofs. I have a picture of 2 angles: angle A and angle B. I need the conclusions and the justifications to prove that angle A + angle B equals 180.


Hi Lisa;
I need more information.  The definition of a flat plane is that it is 180-degrees.  However, you are not telling me that this is a flat plane.
Flat plane itself does not have any degree.

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Parviz F. | Mathematics professor at Community CollegesMathematics professor at Community Colle...
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Only reason that I can think of if from a point of intersection , center point, draw any circle the central angle inscribed of a straight has opposite arc of 180°.
  Half of a full revolution will intersect the circle along diameter with a central angle congruent to
   360°/ 2= 180°