Q1 of 45 Page 27

In figure 3.8, ∠ACD is an exterior angle of ΔABC. ∠B = 40°, ∠A = 70°. Find the measure of ∠ACD.

Given, ∠A = 70° and ∠B = 40°


In a triangle ABC,


The measure of an exterior angle of a triangle is equal to the sum of its remote interior angles


∠ACD is an exterior angle of triangle ABC


So, from theorem of remote interior angles,


∠ACD = ∠BAC + ∠ABC


⇒ ∠ACD = ∠A + ∠B


⇒ ∠ACD = 70° + 40° = 110°


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