This question is concerning the cyclic quadrilateral rule. My question is :
Is it possible to use the cyclic quadrilateral rule if the quadrilateral is in a semi-circle.
To make it more clear I have attached a diagram, so in the diagram, is it right to say that x+y=180 and 6q=180.
I would say no.
Because for the original diagram, the quadrilateral, although in a semicircle, is also in a full circle afterall.
But when any of the four angles in not on the circumference of a full circle.
There is a rule that if an angle is formed at center of circle, then it is twice the angle formed on the circumference.... both angles formed from same points.
So, for what you last asked, 0.5[angle at centre] + [opposite angle] = 180