Question 490711
If the points are really the vertices of a square, then 
AB to AC are perpendicular, or else,
AB to AD are perpendicular
also,
CD to CA are perpendicular, or else
CD to CB  are perpendicular
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Find the equations for the pairs of points:
AB
{{{(y - (-13)) / ( x - 6) = (2 -(-13)) / (-2 - 6) }}}
{{{ y + 13 = 15*(x - 6) }}}
{{{ y = 15x - 103 }}}
AC
.....
Once you find the perpendicular lines, you can
draw an approximate square. 
remember that slopes that are perpendicular
are related as {{{ m[1] = -1/m[2] }}}
The points that form diagonals will be obvious.