Question 113

In a triangle ABC, AB = AC, LBAC = 40° Then the external angle at B is :

Solution

Since AB = AC => $$\angle$$ACBC = $$\angle$$ACB

In $$\triangle$$ABC

=> $$\angle$$ABC + $$\angle$$ACB + $$\angle$$BAC = 180°

=> 2$$\angle$$ABC = 180° - 40° = 140°

=> $$\angle$$ABC = 70°

To find : $$\angle$$ABD = 180° - $$\angle$$ABC

= 180° - 70° = 110°

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