Find the coordinates of the circumcenter for def with coordinates d(1,1), e(7,1) and f(1,5)

First plot those points. You should see a *right* triangle, with sides:

4 vertical and 6 horizontal

So, the circumcenter is the mid point of the hypotenuse of the triangle, because it is a right triangle (otherwise is really harder).

The mid point of F and E:

CIRCUMCENTER = (F+E)/2 = ( (1,5)+(7,1) ) / 2 = (8,6)/2 = (4,3)

ANSWER (4,3)