H
E
E
L
E
M
E
N
T
S
let BC, EF be joined.
Now, since the circles ABC, DEF are equal,
their radii are equal.
Thus
the two straight lines BG, GC are equal to the two straight lines EH, HF; and the angle at G is equal to the angle at H;
therefore
the base BC is equal to the base EF. [I.4]
