Circle Geometry, SMB-019

The diagram shows a large semicircle with diameter    and two smaller semicircles with diameters    and  , respectively, where    is a point on the diameter  . The point    is the centre of the semicircle with diameter  .

The line perpendicular to    through    meets the largest semicircle at the point  . The points    and    are the intersections of the lines    and    with the smaller semicircles. The point    is the intersection of the lines    and  .
 

Explain why is a rectangle.   (3 marks)