Answer:
for n ≤ 3
we are going to put a circle on the 3 and make it filled in then you are going to start an arrow starting from the 3 going to the left all the way to the -10.
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

Angles ABD and CBD are supplementary, so

and the answer is E.
Triangle classification by sides would be scalene, no congruent sides; isosceles, at least 2 congruent sides; equilateral, 3 congruent sides.