Question 1082342
The centroid of a triangle is calculated from the vertices using,
{{{x[c]=(x[1]+x[2]+x[3])/3}}}
{{{y[c]=(y[1]+y[2]+y[3])/3}}}
Substituting,
{{{9=(0+6+x[3])/3}}}
{{{x[3]+6=27}}}
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{{{-3=(-8+0+y[3])/3}}}
{{{y[3]-8=-9}}}
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Solve for {{{x[3]}}} and {{{y[3]}}}.