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jmc

geometry junior

Problem

Two angles of an isosceles triangle measure and . What is the sum of the three possible values of ?
(A)
(B)
(C)
(D)
Solution
There are 3 cases: where is a base angle with the as the other angle, where is a base angle with as the vertex angle, and where is the vertex angle with as a base angle. Case 1: is a base angle with the as the other angle: Here, , since base angles are congruent. Case 2: is a base angle with as the vertex angle: Here, the 2 base angles are both , so we can use the equation , which simplifies to . Case 3: is the vertex angle with as a base angle: Here, both base angles are , since base angles are congruent. Thus, we can use the equation , which simplifies to . Adding up all the cases, we get , so the answer is .
Final answer
D