!---Just for personal reference
Diagram shows a straight line , a circle, congruent quadrants and , and straight lines extended from the ends of each arc. The top centre circle is tangent to the upper line at and the two quadrants at the marked points.
and are collinear
The relation between :
Using Pythagorean Theorem
Note :The figure is symmetrical about the vertical diameter line of the circle (ignoring extra lines and points)