Answer :

Since an entire triangle equals 180 degrees and angle B is 51 meaning B and C are equal so if you add those together and subtract it from 180 the correct answer is A.
Importance
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Short answer: A: 78 °

Why?

Well, when we have a triangle, we have to add up all the angles to be able to have 180°. So, we have an isosceles triangle, we know that an isosceles triangle has two equal sides. We have two unknown sides, but we know that side C is also 51°. When we add both of them up, we have 102. Which of the answer choices make it add up to 180? 78.

Hope this helped you! ♥

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