I haven't got your problem but i presume that you haven't got the question and need an explanation. So it basically says ABC is a triangle with a,b,c being the sides of the triangle a is the side length opposite to vertex A...so on and by knowing properties of triangles 2 formulas you get the ans D{delta or area}=abc/4R D{Delta or area}=rS [S=a+b+c/2] if ya know that much easy peasy lemon squeesy