Question 4 In ΔABC, if BC =AB and ∠B=80∘ then ∠A is equal to (A) 80∘ (B) 40∘ (C) 50∘ (D) 100∘
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Solution
Given ΔABC such that BC = AB = and ∠B=80∘ InΔABCAB=BC⇒∠C=∠A [angles opposite to equal sides are equal] We know that the sum of all the anlges of a trianlge is 180∘ ⇒∠A+∠B+∠C=180∘⇒∠A+80∘+∠A=180∘⇒2∠A=180∘⇒2∠A=180∘−80∘=100∘⇒∠A=100∘2⇒∠A=50∘