Question
Find the third vertex of triangle whose centroid is origin and two vertices are (2, 4, 6) and (0, -2, -5).

Answer

Let the third or unknown vertex of $\triangle\text{ABC}$ be A(x, y, z).
Other vertices of triangle are B(2,4, 6) and C(0, -2, -5).
The centroid is G(0, 0, 0).
$\therefore(0,0,0)=\Big(\frac{2+0+\text{x}}{3},\frac{4-2+\text{y}}{3},\frac{6-5+\text{z}}{3}\Big)$
On comparing coordinates, we get,
$\frac{2+\text{x}}{3}=0,\frac{2+\text{y}}{3}=0\ \text{and}\ \frac{1+\text{z}}{3}=0$
$\Rightarrow\text{x}=-2,\ \text{y}=-2\ \text{and}\ \text{z}=-1$

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