Question

show how to construct circumcircle of a triangle

Answer 1

Circumference of a triangle means its perimeter

So, sum of three sides of triangle is its perimeter (circumference)

actually circumference word is used for circles not for triangles

Answer 2

take a triangle ABC draw a perpendicular from line AB draw perpendicular and from BC draw perpendicular to lines intersects at O. take the O as the centre and OA as the radius and draw a circle.