Question

BD is a diameter of circle O. If m∠ACB = 30°, what is m∠DBA?

Answer 1

it is 60

Explanation:

Answer 2

m∠DBA = 60º

Explanation:

Angle subtended by the diameter is 90º :

⇒ m∠DAB = 90º

Angles in a circle formed by the same arc are equal :

⇒ ∠ ADB = ∠ACB

⇒ m∠ ADB = 30º

Sum of angles in a triangle is 180º :

⇒ m∠DBA + m∠DAB + m∠BDA = 180º

⇒ m∠DBA = 180° - 90° - 30°

⇒ m∠DBA = 60°