check here.

來源: 於 2016-11-07 19:41:24 [舊帖] [給我悄悄話] 本文已被閱讀：次

EF//AB, easy to see EFG and AGB are both equalaterals;
both angle ADB and ABD are 50, so AD=BD, SO AD=AG
with these info, you can get all angles (in blue colors),
and draw conclusion easily.