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GRE circle question


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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 by Eigen
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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

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