If isosceles triangle ABC has a 130° angle at vertex B, which statement must be true?

The angles in a triangle add to 180°, so ∠A + ∠C = 180° − 130° = 50°. Since the triangle is isosceles and neither ∠A nor ∠C can be 130°, those two angles must be equal, making each 25°. Therefore, m∠A + m∠B = 25° + 130° = 155°, so the statement that must be true is “m∠A + m∠B = 155°.”

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