Question 1134748
<pre><font size=4><b>{{{drawing(400,400,-6,6,-6,6, grid(1),
circle(2,3,.1),
circle(0,-3,.1), locate(2,3,"E(2,3)"), locate(0,-3,"F(0,-3)") )}}}

Draw a vertical rectangle with those points at opposite corners.

{{{drawing(400,400,-6,6,-6,6, grid(1),
circle(2,3,.1), blue(line(0,3,0,-3),line(0,3,2,3),line(0,-3,2,-3),line(2,-3,2,3)),

circle(0,-3,.1), locate(2,3,"E(2,3)"), locate(0,-3,"F(0,-3)") )}}}

Now draw horizontal rectangle just like it to make a big "plus" sign:

{{{drawing(400,400,-6,6,-6,6, grid(1),
circle(2,3,.1), blue(line(0,3,0,-3),line(0,3,2,3),line(0,-3,2,-3),line(2,-3,2,3),
line(-2,1,4,1),line(-2,1,-2,-1),line(-2,-1,4,-1),line(4,-1,4,1)),

circle(0,-3,.1), locate(2,3,"E(2,3)"), locate(0,-3,"F(0,-3)") )}}}

Draw in the square:

{{{drawing(400,400,-6,6,-6,6, grid(1),
circle(2,3,.1), blue(line(0,3,0,-3),line(0,3,2,3),line(0,-3,2,-3),line(2,-3,2,3),
line(-2,1,4,1),line(-2,1,-2,-1),line(-2,-1,4,-1),line(4,-1,4,1)),
red(line(2,3,4,-1),line(4,-1,0,-3),line(0,-3,-2,1),line(-2,1,2,3)),
circle(0,-3,.1), locate(2,3,"E(2,3)"), locate(0,-3,"F(0,-3)") )}}}

Now you can see that they are (4,-1) and (-2,1)

Edwin</pre></font></b>