Question 348877
{{{ABG+GBF+FBC=180}}}
{{{A3+A3+A1=180}}}
{{{2*A3+A1=180}}}
{{{A1=180-2*A3}}}
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{{{BCF+FCE+ECD=180}}}
{{{A2+A4+A4=180}}}
{{{2*A4+A2=180}}}
{{{A2=180-2*A4}}}
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{{{A1=A2}}}
Substituting,
{{{180-2*A3=180-2*A4}}}
{{{highlight(A3=A4)}}}