Question 877561
{{{A+B+C=180}}}
{{{3x+1+4x-17+5x-20=180}}}
{{{12x=216}}}
{{{x=18}}}
{{{A=3x+1=54+1=55}}}
{{{B=4x-17=72-17=55}}}
{{{C=5x-20=70}}}
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ABC is an isosceles triangle.