Question 83353
You know two key factors:
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1. The sum of the angles in a triangle is 180 degrees
2. In an isosceles triangle, 2 of the angles are equal.
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Let's first suppose that the 50 degrees is the odd angle in that it is NOT one of the pair
of equal angles.  Therefore, we can subtract 50 degrees from the 180 degrees in the 
triangle and find that the remaining pair of equal angles must total to the missing
130 degrees.  So each of the remaining angles must be 1/2 of 130 degrees or 65 degrees.
So, in this case the three angles in the triangle are a = 50 degrees (given), b = 65 degrees, 
and c = 65 degrees.
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Another possibility exists.  This possibility is that one of the other angles in the triangle
is equal to the given 50 degree angle.  Therefore, this triangle has two angles of 50 
degrees each for a total of 100 degrees.  This time the "odd" angle has to be the remaining
number of degrees in the triangle.  The odd angle measure is 180 - 100 = 80 degrees.
So in this triangle the angles are a = 50 degrees (given), b = 50 degrees, and c = 80 degrees
OR a = 50 degrees (given), c = 50 degrees, and b = 80 degrees. (Two cases depending
on the values you select for b and c.)
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Hope this helps you to understand how to find the three possible answers to the problem.  Cheers!