If →OA=^i−^j and →OB=^j−^k, then a unit vector parpendicular to the plane AOB is
If →r×→b=→c×→b and →r.→a=0 where →a=2^i+3^j−^k,→b=3^i−^j+^k and →c=^i+^j+3^k, then →r is equal to