Step-by-step explanation: As we can see in the figure below, angles 2 and 4 are <u>Vertical</u> <u>Angles</u>, i.e., they are angles opposite each other when two lines cross. Vertical angles are always congruent.
BA and BD are radii of the circle, so triangle ABD is isosceles. Then angles BDA and BAD are congruent, and the remaining (central) angle ABD has measure