(l2 + m2) + (m2 + n2) + (n2 + l2) + (2lm + 2mn + 2nl)= l2 + l2 + m2 + m2 + n2 + n2 + 2lm + 2mn + 2nl= 2l2 + 2m2 + 2n2 + 2lm + 2mn + 2nl