ABCD-paralelogram
⇒AB║DC; BC║AD⇒AB=DC; BC=AD (1)
⇒∡A=∡C; ∡B=∡D (∡opuse) (2)
⇒∡ alaturate unei laturi sunt suplementare (=180°) (3)
⇒m(∡A)+m(∡B)+m(∡C)+m(∡D)=360° (4)
AB=BC+3cm
P=50cm
din (1)⇒AB=DC=BC+3cm
P=AB+BC+CD+AD
P=BC+3cm+BC+BC+3cm+BC
P=4BC+6cm
4BC+6cm=50cm
4BC=50cm-6cm
4BC=44cm
⇒BC=44cm/4=11cm
⇒AB=DC=BC+3cm=11cm+3cm=14cm
⇒BC=AD=11cm
din (2) si (3) ⇒m(∡B)=m(∡D)=130°
⇒m(∡A)=m(∡C)=180°-130°=50°
