SOLUTION: I'm looking at an obtuse triangle (ACB) on a protractor. the measurement of angle A measures 110 degrees. Sides AB and AC are congruent. How do I find the measurement of angle B

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Question 179758: I'm looking at an obtuse triangle (ACB) on a protractor. the measurement of angle A measures 110 degrees. Sides AB and AC are congruent. How do I find the measurement of angle B?
Answer by solver91311(24713) About Me  (Show Source):
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If the two sides adjacent to angle A are congruent, then the triangle must be isoceles by definition. If the triangle is isoceles, then the other two angles must also be congruent, that is, equal in measure -- again by definition of isoceles. The sum of the interior angles of any triangle is 180 degrees. So, if angle A measures 110 degrees the sum of the other two angles must be 180 - 110 = 70 degrees. Since the other two angles are equal in measure, each one accounts for half of the 70 degrees. Therefore angle B (and angle C for that matter) measures 35 degrees.


John