O foaie de tabla avand forma unui semidisc de diametru AB= 12 dm. Punctele C,D,E,F,G impart semicercul in sase arce egale.Demonstrati ca ADFB - trapez
isoscel
vezi figura arcele AC=CD=DE=EF=FG=GB=180/6=30 arcele AD=DF=FB=2X30=60⇒< AOD=<DOF=<FOB=60 segmentele AO=OD=OF=OB=R⇒ΔADO=ΔDOF=ΔFOB=Δechilaterale⇒AD=FB <DFO=<FOB=60⇒DF paralel AB⇒ADFB= trapez isoscel