Question

I added photo.Book said answer is 60 degree but how get it explain me plz

Answer 1

Hope it will be helpful to you....

Answer 2

it is because od property of circle that "Angle formed on same  segment  are equal in measure so ,

As △ABC is equilateral

∴   ∠ABC = 60°

  ∠ADC = ∠ABC (Angles in the same segment)

∴  ∠ADC =  60°