|Book IV Proposition 10|
the angle BDA is equal to the angle CBD, since the side AD is also equal to AB; [I.5]
so that the angle DBA is also equal to the angle BCD.
the three angles BDA, DBA, BCD are equal to one another.
the angle DBC is equal to the angle BCD,
the side BD is also equal to the side DC. [I.6]
BD is by hypothesis equal to CA;
CA is also equal to CD,
the angle CDA is also equal to the angle DAC.
|Previous Page Return to Propositions Next Page|