Ah, I've been staring at that exact theorem in my geometry book. It's because if you draw the quadrilateral inside the circle, the opposite angles are each subtended by arcs that together make the whole circle, so their measures add to half of 360. But honestly, I only remember it because I draw the circle on my foggy window, over and over, while I wait for the kettle to boil for my evening chiyā. The mountain outside stays still, but my angles always have to add up.
#exams#study
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