Explanation
We have,
Point
$$ A\left( {{x}_{1}},{{y}_{1}},{{z}_{1}} \right)=\left( 2,2,-3 \right) $$
$$ B\left( {{x}_{2}},{{y}_{2}},{{z}_{2}} \right)=\left( 5,6,9 \right) $$
$$ C\left( {{x}_{3}},{{y}_{3}},{{z}_{3}} \right)=\left( 2,7,9 \right) $$
Let the coordinates of point $$D\left( x,y,z \right).$$
So,
According to question,
$$ AB=\sqrt{{{\left( 5-2 \right)}^{2}}+{{\left( 6-2 \right)}^{2}}+{{\left( 9-3 \right)}^{2}}} $$
$$ AB=\sqrt{9+16+149}=\sqrt{{{13}^{2}}}=13 $$
$$ AC=\sqrt{{{\left( 2-2 \right)}^{2}}+{{\left( 7-2 \right)}^{2}}+{{\left( 9+3 \right)}^{2}}} $$
$$ AC=\sqrt{0+25+144}=\sqrt{169}=13 $$
Thus $$ABC$$ is isosceles triangle with $$AB=AC$$
So, angle bisector $$AD$$ bisects $$BC$$
$$D\equiv \left( \dfrac{5+2}{2},\dfrac{6+7}{2},\dfrac{9+9}{2} \right)\equiv \left( \dfrac{7}{2},\dfrac{13}{2},9 \right)$$
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