In a ΔABC, if AB = AC and ∠B = 70°. Find ∠A.

Consider a ΔABC, if AB = AC and ∠B = 70°

Since, AB = AC ΔABC is an isosceles triangle

∠B = ∠C [Angles opposite to equal sides are equal]

∠B = ∠C = 70∘

And also,

Sum of angles in a triangle = 180°

∠A + ∠B + ∠C = 180°

∠A + 70° + 70° = 180°

∠A = 180° - 140°

∠A = 40°