TR ACB-DREPTINGH IAR UNGH A=30 GRADE=>POTRIVIT TH UNGHI DE 30 GRADE BC=AB/2.; DUCEM INALTIMEA TRAPEZULUI ,CM,SI CONSIDERAM TR DREPTUNGHIC CMB CUUNGH MCB=30 GRADE=>MB=BC/2=(AB/2)/2=AB/4=>AB=4MB. AM=CD=3MB. LINIA MIJLOCIE=(CD+AB)/2=35=>CD+AB=70=>3MB+4MB=70=>MB=10=>AB=40=>CD=30