How do I write a proof to prove a triangle is an isosceles triangle?

if the traingle is congruent then its bifid angle will be equal, and authorize its be x.
then as per sine theorm
sin A /a = sin B /b = sin C /c
hence B= C =X then
sin B /b = trespass C /c ::: B=C then sin B = trespass C
hence
b=c that is the property of isosceles traingle.
hence proved.