In the following figure, ∆ABC is an equilateral triangle. Find ∠x.

 

As we know each angle of an equilateral triangle is 60^o.

Therefore, ∠ABC = 60^o

We also know that an exterior angle of a triangle is equal to the sum of its interior opposite angles.

Therefore, ∠ABC = ∠ADB + ∠DAB

⇒ 60^o = x + 30^o

⇒ x = 60^o − 30^o

⇒ x = 30^o