Please solve l 2+m 2+m 2+n 2+n 2+l 2+2lm+2mn+2nl with step methods.
l2+ m2+ m2+ n2+ n2+ l2+ 2lm + 2mn + 2nl
= (l2+2lm+m2) + (l2+2nl+n2) + (m2+2mn+n2)
= (l+m)2+ (l+n)2+ (m+n)2
= (l2+2lm+m2) + (l2+2nl+n2) + (m2+2mn+n2)
= (l+m)2+ (l+n)2+ (m+n)2