a+b+c+d=360 suma masurilor unghiurilor intr-un patrulater convex=360°
a/1/2=b/1/3=c/1/6=d/1/7 (Măsura unghiurilor unui patrulater convex ABCD invers proporționale cu 1 supra 2, 1 supra 3, 1 supra 6, 1 supra 7)
a/2=b/3=c/6=d/7=k
a=2k, b=3k, c=6k, d=7k dar a+b+c+d=360
2k+3k+6k+7k=360
18k=360⇒k=20
a=2k=2×20=40°
b=3k=3×20=60°
c=6k=6×20=120°
d=7k=7×20=140°
