Explicație pas cu pas:
a) fie BT ⊥ DC si AF ⊥DC ==> ABTF dreptunghi ==> FT = AB = 7
==> DF=TC = (DC-7)/2= (55-7)/2 = 48/2 = 24 cm
BT, AF = inaltimi in trapez ==> BT = 18 cm
==> Pitagora BC= √(324+576) = √900=30cm
b) cu pitagora ==> TC=DF= √(289-64) =√225= 15 cm
==> DC= DF+FT+TC = => 40= 2*15+ FT
==> FT = 40-30 = 10 cm
ABTF = dreptunghi ==> AB=FT ==> AB= 10 cm