$\"\"$

The coordinates of the triangle $\"\"$ are $\"\"$ .

The x-coordinate of D is the mean of the x-coordinates of the vertices of $\"\"$ .

Let $\"\"$ , $\"\"$ and $\"\"$ .

Mean of x-coordiantes of $\"\"$

$\"\"$ (Mean of x-coordiantes)

$\"\"$ (Substitute $\"\"$ )

$\"\"$ (Simplify) $\"\"$

The y-coordinate of D is the mean of the y-coordinates of the vertices of $\"\"$ .

Mean of y-coordiantes of $\"\"$

$\"\"$ (Mean of x-coordiantes)

$\"\"$ (Substitute $\"\"$ )

$\"\"$ (Simplify) $\"\"$

The coordinates of D are $\"\"$ .