In the figure shown, the length of minor arc SD is one-half the length of minor arc FD. Find the measure of ∠SDG in degrees.
arc(FD) = 2·76o = 152o
arc(GF) = 2·40o = 80o
arc(GSD) = 2·64o = 128o
arc(SD) = ½·arc(FD) = 76o
arc(SG) = arc(GSD) - arc(SD) = ...
angle(SDG) = ½·arc(SG) = ...