How to Prove Thales???s Theorem

Now draw a line — its length equal to the diameter of the circle — through its center:

The length of line AB is equal to the diameter of the circle.

The length of AB is equal to the diameter of the circle

Choose a point somewhere on the circle (but not on the line), and call it C.

We now have a circle with point A, B and C. A and B form a straight line with O, the center of the circle.

And finally, draw lines AC and BC:

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