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BOOK I. PROP. XV. THEOR.
15
F two right lines (
and 
) intersect one another, the vertical angles 
and 
, 
and 
are equal.
= = 
= =
∴ = .
In the same manner it may be shown that
=
Q.E.D.
Page:First six books of the elements of Euclid 1847 Byrne.djvu/49
