T H E E L E M E N T S |
Book III Proposition 32 | |
Next, since ABCD is a quadrilateral in a circle, its opposite angles are equal to two right angles. [III.22] But the angles DBF, DBE are also equal to two right angles; therefore the angles DBF, DBE are equal to the angles BAD, BCD, of which the angle BAD was proved equal to the angle DBF; therefore the angle DBE which remains is equal to the angle DCB in the alternate segment DCB of the circle. |
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