



 
Question from Carla, a student: PQRS is a rectangle. A semicircle drawn with PQ as diameter cuts RS at A and B. Remember that any arc on a circle is subtended by an angle from the circumference which is half of the measure of the angle from the circle's center, then you can quickly draw the corresponding central angle: Notice that the two blue lines are the same length, so use your knowledge of the ratios of a 306090 triangle to determine the length of the blue line in the right triangle inside. Cheers,
 


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