To illustrate that perpendicular bisectors of the sides of a triangle concur at a point(called the circumcentre) and it falls inside for an acute-angled triangle, on the hypotenuse of right-angled triangle and outside for an obtuse-angled triangle.
Circumcentre of a triangle is the point of intersection of all the three perpendicular bisectors of the sides of a triangle. It is where the "perpendicular bisectors" (lines that are at right angles to the midpoint of each side) meet. The circumcentre of a triangle is equidistant from its vertices and the distance of the circumcentre from each of the three vertices are called circum-radius of the triangle.
Fig (a) Fig (b)