Bonsoir,

EX1

1) FE = BC donc OB + FE = OB + BC = OC (relation de Chasles).

2) AB + BC = AC

3) AB - BC = AB + CB

or CB = OA donc AB - BC = AB + OA = OB

4) BA = OF donc EO + BA + FA = EO + OF + FA = EA

5) -EF = FE = BC donc  DB - EF = DB + BC = DC