Question 1201977
Draw a perpendicular to the triangle.

QM passes through the cebtre and bisects the chord

QMP is right triangle
apply pythagoras theorem

sqrt(26^2-10^2)=24
Height of triangle = 24

Radius of circumcircle = Product of side / 4 * area of triangle

(26*26*20)/(4 * 240) = 14.08 cm  You round off 

*[illustration circumcircle.png].