Question 1087674
<pre>
{{{drawing(400,3600/11,-2,9,-2,7,
graph(400,3600/11,-2,9,-2,7),
triangle(1,1,7,1,1,5),
red(circle(4,3,sqrt(13))),
locate(1,1,"D(1,1)"), locate(7,1,"E(7,1)"),locate(1,5.5,"F(1,5)") )}}}

The circumcenter is where the perpendicular bisectors of the sides
intersect. Two of them are very easy to draw, since the longer leg
is horizontal and the shorter one is vertical.  I'll draw them in green:

{{{drawing(400,3600/11,-2,9,-2,7,
graph(400,3600/11,-2,9,-2,7),
triangle(1,1,7,1,1,5),
red(circle(4,3,sqrt(13))),
green(line(4,-20,4,20),line(-20,3,20,3),locate(4.1,3.5,"C(4,3)")),
locate(1,1,"D(1,1)"), locate(7,1,"E(7,1)"),locate(1,5.5,"F(1,5)") )}}}

So you can see it's C(4,3).

Edwin</pre>