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6
BOOK I. PROP. VI. THEOR.
N any triangle (
) if two angles (
and 
) are equal, the sides (
and 
) opposite to them are also equal.
For if the sides be not equal, let one of them be greater than the other , and from it cut off 
= (pr. 3.), draw 
.
Then in 
and , = , (conft.) = (hyp.) and 
common, ∴ the triangles are equal (pr. 4.) a part equal to the whole, which is absurd; ∴ neither of the sides or is greater than the other, ∴ hence they are equal
Q.E.D.
