In the figure AB = AC and ∠ACD = 110° find A.

            ∠ACB + ∠ACD = 180° ...... (Linear pair)
         ... 󐫋 + 110° = 180°
⇒ ∠ACB = 180° - 110° = 70°
      Since in ΔABC, AB = AC
                   ഋ = ∠C = 70°
Now, in ΔABC, we have
          ∠A + ∠B + ∠C = 180° ...... (Sum angles)
     ... ഊ + 70° + 70° = 180°
    ...ഊ = 180° - 140° = 40°