Therefore, using the above relations, together with the similar ones employed in Theorem 1 concerning X i,j,k and X i,j , it all boils down to expressing in terms of segment lengths X 2,1,1,2 , X 2,1,2,2 , X 2,2,1,2 , and ZC2 5 . Finally, by performing some algebraic manupilations with the excess terms, the demonstration is completed.