∡bcd=180-dbc-bdc=180-70-30
∡bcd=80°
∡bad=(360-2∡bcd)/2=(360-160)/2
∡bad=100°
∡adb=180-∡abd-∡bad=180-50-100
∡abd=30°
∡abc=50+70=120°
∡bcd=80°
∡cda=30+30=60°
∡dab=100°
arc(ab)=2 x ∡adb=60°
arc(bc)=2 x ∡bdc=60°
arc(cd)=2 x dbc=140°
arc(da)=2 x ∡abd=100°