Radius: R = a/2sinα. a - lenght of any side of triangle, α - the angle opposite this side. R = abc/P. a, b, c - lenghts of side of the triangle, P - area of the triangle. If one of the sides of the triangle is the diameter then the triangle inscribed in a circle is right. For the triangle inscribed in a circle, center of this circle get draw an axes of symmetry for the sides of triangle.