T H E E L E M E N T S |
Book III Proposition 37 | |
Now, since DE touches the circle ABC, and DCA cuts it, the rectangle AD, DC is equal to the square on DE. [III.36] But the rectangle AD, DC was also equal to the square on DB; therefore the square on DE is equal to the square on DB; And FE is equal to FB; therefore the two sides DE, EF are equal to the two sides DB, FB; and FD is the common base of the triangles; therefore the angle DEF is equal to the angle DBF. [I.8] |
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