Explanation
Since, the centroid divides the line joining the orthocentre and circumcentre in the ratio $$2:1$$
The coordinates of the centroid will be,
($$ \dfrac{9}{3} , \dfrac{9}{3}, \dfrac{12}{3} $$)
$$= (3,3,4)$$
Given, $$A=(1,2,-3), G(-3,4,5)$$
Therefore, $$AG=\sqrt { { (-3-1) }^{ 2 }+{ (4-2) }^{ 2 }+{ (5-(-3)) }^{ 2 } } $$
and $$ AG=\sqrt { 84 } =2\sqrt { 21 } $$
$$P$$ is the centroid of $$\triangle BCD$$
So, $$G$$ divides $$AP$$ in $$3:1$$.
Let $$AG=3x$$, then $$GP=x$$
$$3x=2\sqrt { 21 } \\ x=\dfrac { 2\sqrt { 21 } }{ 3 } $$
Now $$AP=AG+GP$$
$$\Rightarrow AP=3x+x$$
$$ \Rightarrow AP=4x$$
$$ \Rightarrow AP=4\left( \dfrac { 2\sqrt { 21 } }{ 3 } \right) =\dfrac { 8\sqrt { 21 } }{ 3 } $$
So, option A is correct.
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