Question 823853
a. Construct the perpendicular bisectors of each side. 
The perpendicular bisector of a segment (such as the side of a triangle) is the line whose points are at the same distance from both ends of the segment.
The perpendicular bisectors of the sides of a triangle intersect at one point that is at the same distance from the three vertices.
Using that distance as the radius, and that intersection point as the center,
you can construct a circle that passes through the three vertices.
That is the circle circumscribed about the triangle.
You do not need to construct all 3 perpendicular bisectors.
It is enough to construct two of them.
Where those two intersect, the third one will go through that point too.