Question 890195
<pre><font size = 6><b>

Three possibilities for the 4th vertex D:

  D(4,-1)             D(4,5)            D(-2,-5)
{{{drawing(400/3,200,-3,5,-6,6,grid(1),

green(line(1,0,1,-3),line(1,-3,4,-1),line(4,-1,4,2),line(1,0,4,2)))}}}          {{{drawing(400/3,200,-3,5,-6,6,grid(1),

green(line(1,0,1,-3),line(1,-3,4,2),line(4,5,4,2),line(1,0,4,5)))}}}          {{{drawing(400/3,200,-3,5,-6,6,grid(1),

green(line(1,0,-2,-5),line(1,-3,-2,-5),line(1,-3,4,2),line(1,0,4,2)))}}}
  D(4,-1)             D(4,5)            D(-2,-5)
Edwin</pre></font></b>