check here.

來源: longsky 於 2016-11-07 19:41:24 [] [舊帖] [給我悄悄話] 閱讀數 : (228 bytes)

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.

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