If O and O' denote respectively the circumcentre and orthocentre of ΔABC, then $\vec{O'A} + \vec{O'B} + \vec{O'C} =$

$\vec{O'O}$ $\vec{OO'}$ $2\vec{OO'}$ $2\vec{O'O}$

$2\vec{O'O}$

Replacing S by O', we get $\vec{O'A} + \vec{O'B} + \vec{O'C} =3\vec{O'G}$ $⇒\vec{O'A} + \vec{O'B} + \vec{O'C} =2\vec{O'G}+\vec{O'G}$ $⇒\vec{O'A} + \vec{O'B} + \vec{O'C} =2\vec{O'G}+\vec{GO}$   $[∵O'G=2GO]$  $⇒\vec{O'A} + \vec{O'B} + \vec{O'C} =\vec{O'O}$