Răspuns:
Explicație pas cu pas:
AM =BC/2
20=BC/2 ⇒BC=2*20=40 cm
AM=BM=MC =BC/2 =40/2 =20 cm
∡B =90-BAD =90-30 =60°
ΔBAC = drept ;∡B=60° ⇒∡C=30°
AM=MC⇒ΔAMC = isoscel
∡BMA=60°⇒∡AMC =120°⇒∡C=CAM =(180-120):2 =30°
∡DAM=∡A-BAD-CAM =90-30-30=30°
⇒∡BAM=BAD+DAM=30+30=60°
⇒ΔBAM = echilateral
⇒AB=AM=BM =20 cm
AC²=BC²-AB²=40²-20²=1600-400 =1200
AC=√1200 =20√3 cm
ΔABM =echilat.⇒BD=DM =BM/2 =20/2 =10 cm
CD=BC-BD=40-10=30 cm
AD²=BD*CD=10*30 =300
AD=√300 =10√3 cm