GRE circle question

[dux3000]

For this question (http://www.greenlighttestprep.com/module/gre-geometry/video/889) I understand the video solution however when I solved it, I used the fact that angle AOB = angle ADB to get A (50 degrees) as my answer. Not sure what happened

 

[Eigen]

Angle AOB does not = angle ADB.

ABO is 90, so AOB is 50. AOB + BOD = 180, so BOD = 130. OB and OD are both the same length (radii of circle), so OBD = ODB = 180-130/2 = 25.

OBC = 90, so OBD + DBC = 90, or DBC = 65.

::edit:: Just realized my solution was the same as the video (didn't watch it). So what exactly are you asking?

Edited September 10, 2015 by Eigen

[dux3000]

I thought there was a rule I learned in highschool that says if you have a tangent line then you get an isosceles triangle (so angle AOB = angle ADB). BUT I just looked it up and I'm wrong. It has to do with having 2 tangent lines from the same point. 

Back to studying!!

Thanks though