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Book I   Proposition 22
Let there be set out a straight line DE, terminated at D
but of infinite length in the direction of E, and
    let DF be made equal to A,
    FG equal to B,
and
    GH equal to C. [I.3]

With center F and distance FD
    let the circle DKD be described;
again, with center G and distance GH
    let the circle HKH be described;
and
    let KF, KG be joined;

I say that the triangle KFG has been constructed out of three straight lines equal to A, B, C.
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