(This problem is from CE Ref V4 of Gillesania)
A quadrilateral ABCD is inscribed in a semicircle with side AD as the diameter. If point O is the center of the diameter, determine the angle DCO if angle CAD is 39 deg.
In the book's solution, it says that angle COD = 2 times angle CAD. Is this a rule in semi circles?
(Attached is the drawn image of the problem)
Thanks in advance sirs.