Question 370056
{{{drawing(300,300,-10,10,-10,10,circle(0,0,5),circle(0,0,0.3),line(0,-5,0,5),line(-10,5,10,5),line(-10,-5,10,-5),circle(8,5,0.2),circle(-8,-5,0.2),locate(8,5,C),locate(-9,-5,D),locate(0,6,A),locate(0,-5,B))}}}
.
.
Since AC is a tangent, then the angle between AC and AB is 90 degrees. 
Same for the angle between BD and AB. 
{{{CAB=ABD=90}}}
They are alternate interior angles and since they are equal, AC is parallel to BD.