Can you see again my solution ?. Maybe you missed something.
Angle A + Angle B + Angle C=180= Angle DEA + DEF + FEC
(Angle A= Angle DEA and Angle FEC=FBC=B as triangle FEC= Triangle FBC)
so we will have Angle C=DEF, but B=C)
so I answered your question. And the word I posted step 1, It doesn't matter. If you don't like to put that word, you can throw it away.
Given that:
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