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In ABC, BC = AB and B = 80^. Then A is equal to

Mathematics

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Step-by-step solution

4 steps
  1. Identify the type of triangle.

    Given that in △ABC\triangle ABC, BC=ABBC = AB, this means that △ABC\triangle ABC is an isosceles triangle.

  2. Apply the property of isosceles triangles.

    In an isosceles triangle, the angles opposite the equal sides are equal. Since side BC is opposite ∠A\angle A and side AB is opposite ∠C\angle C, we have ∠A=∠C\angle A = \angle C.

  3. Use the sum of angles in a triangle.

    The sum of the interior angles in any triangle is 180∘180^\circ.
    So, ∠A+∠B+∠C=180∘\angle A + \angle B + \angle C = 180^\circ.

  4. Substitute the given values and solve for ∠A\angle A.

    We are given ∠B=80∘\angle B = 80^\circ. Since ∠A=∠C\angle A = \angle C, we can substitute ∠A\angle A for ∠C\angle C in the equation:

    ∠A+80∘+∠A=180∘\angle A + 80^\circ + \angle A = 180^\circ 2∠A+80∘=180∘2\angle A + 80^\circ = 180^\circ 2∠A=180∘−80∘2\angle A = 180^\circ - 80^\circ 2∠A=100∘2\angle A = 100^\circ ∠A=100∘2\angle A = \frac{100^\circ}{2} ∠A=50∘\angle A = 50^\circ

    The final answer is \boxed{\text{50^\circ}}.

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