Given: A(2,2,1),B(1,2,2)andC(2,1,2) are vertices of ΔABC.
⇒AB=(2−1)2+(2−2)2+(1−2)2=2
⇒BC=(1−2)2+(2−1)2+(2−2)2=2
⇒CA=(2−2)2+(2−1)2+(1−2)2=2
So, ΔABC is equilateral.
Therefore, orthocentre and centroid will be same.
⇒G≡(32+1+2,32+2+1,31+2+2)
⇒G≡(35,35,35)

Also, mid point of AB is D(23,2,23)
⇒l1=(23−35)2+(2−35)2+(23−35)2
⇒l1=361+91+361
⇒l1=61
Similarly, l2=l3=61
⇒(l1)2+(l2)2+(l3)2=61+61+61
⇒(l1)2+(l2)2+(l3)2=21