Answer:
a) circumcenter
Explanation:
You want to know the name of the point of intersection of the three perpendicular bisectors of the sides of a triangle.
Circumcircle
Each side of a triangle is a chord of the circumscribed circle. The perpendicular bisector of a chord is a line through the center of the circle. Hence the point of concurrency of the perpendicular bisectors of the sides of a triangle is the center of the circumscribed circle.
The name of the center of the circle circumscribing a triangle is "circumcenter."
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Additional comment
When the triangle is a right triangle, the circumcenter is the midpoint of the hypotenuse, which is a diameter of the circle.