Răspuns:
Explicație pas cu pas:
4.∡ADB=90° ∡ADC=∡ABC=120° ⇒∡BDC=120°-90°=30°
∡BDC=∡ABD=30° alt interne
in Δ dreptunghic ABD AD=BC/2 ⇒BC=2AD=2·9m=18m
Pabcd=2(AD+BC)=2(9+18)=2·27=54 m raspuns: a
5
se formeaza Δ isoscel OAB OA=OB=5 cm
ducem OM⊥AB ⇒in Δ dreptunghic OAM OA=ipotenuza=5 cm
AM=AB/2=8/2=4 cm
aplicam Pitagora OM²=OA²-OM²=25-16 ⇒OM=3cm
Aaob=OM·AB/2=3·8/2=3·4=12cm raspuns : c
