All perpendicular bisectors of a triangle concur at one point called circumcenter as a center of its circumscribing circle.
Bisectors of AB and BC meet at O. By ITT, we have 
, hence there’s a circle circumscribing 
Corollary 1
All 3 bisectors of 3 sides of a triangle concur at ONE point called circumcenter.
There’s a unique line from O to mid-point of AC. By ITT, it must perpendicular to AC.
Corollary 2
The midpoint of hypotenuse of a right triangle is the center of its circumscribed circle
Draw a circle with diameter as one side of a triangle whose 3rd virtex in on the circle. Now we need to prove it is a right triangle.
By ITT, we have
As sum of all angles in a triangle is 1800, so
Hence it is a right triangle.