To form the Arco Capaz, start with segment AB and angle CAB. Draw line through A perpendicular to AC. Draw perpendicular bisector to AB. Obtain the point O of intersection on these two new lines. Draw the circle centered at O passing through A. If E is on the arc of the circle between A and B (on the opposite side of AB from C), then the angle measure of AEB is equal t the measure of CAB.
In the following applet you can drag points A, B, C, and E to move the figure.
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