T H E E L E M E N T S |
Book III Proposition 32 | |
Then, since a straight line EF touches the circle ABCD at B, and BA
has been drawn from the point of contact at right angles to the tangent, the center of the circle ABCD is on BA. [III.19] Therefore BA is a diameter of the circle ABCD; therefore the angle ADB, being an angle in a semicircle, is right. [III.31] |
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