$I n Δ A B C, BC = AB and ∠ B = 80^{\circ} . T h e n, ∠ A = ? (a) 50^{\circ} (b) 40^{\circ} (c) 100^{\circ} (d) 80^{\circ}$

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Solution

ANSWER:
Given: In ∆ ABC, BC = AB and ∠ B = 80°.
In ∆ ABC,
As, AB=BC
⇒∠A=∠C
Let ∠A=∠C=x
Using angle sum property of a triangle,
∠A+∠B+∠C=180°⇒x+80°+ x=180°⇒2x=180°-80°⇒2x=100°
⇒x=100°2⇒x=50°⇒∠A=50°
Hence, the correct option is (a).

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