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Interior angles of a polygon

  1. Aug 13, 2016 #1
    1. The problem statement, all variables and given/known data
    bandicam 2016-08-14 00-45-30-451.jpg

    2. Relevant equations
    sum interior angles (n-2)*180
    angles of a quadrilateral: a+b+c=d = 360


    3. The attempt at a solution
    What do you do with the exterior angle?
    80+130+a+x=360
     
  2. jcsd
  3. Aug 13, 2016 #2

    Ray Vickson

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    How would you find ##x## from the information in the diagram?
     
  4. Aug 13, 2016 #3
    a+130+x=360
    180-100=80
    x=80
    130+80+85= 295
    360-295=65
    a=65
     
  5. Aug 13, 2016 #4

    Ray Vickson

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    Much easier: just use the fact that 100+x = 180, because the angles 100 and x make up a straight line. (I know you got the correct value for x above, but I found your argument to be confusing and not as step-by-logical-step as it should be.)
     
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