If `overset(to)(a) , overset(to)(b) " and " overset(to)(c ) ` are three non- coplanar vectors then
`(overset(to)(a) + overset(to)(b) + overset(to)(c )) . [( overset(to)(a) + overset(to)(b)) xx (overset(to)(a) + overset(to)(c ))]` equals