problema 2- a)
cum demonstrez ca acele drepte sunt paralele?

a) AD/AB=4/12=1/3, AE/AC=3/9=1/3, deci AD/AB=AE/AC⇒ΔABC asemenea cu
ΔADE⇒ DE║BC
b) DE/BC=1/3 (coeficientul de proportionalitate), DE/12=1/3, DE=12/3=4 cm