A unit vector coplanar with →i+→j+3→k and →i+3→j+→k and perpendicular to →i+→j+→k is
1√2(i+j)
1√3(→i+→j+→k)
1√2(→j−→k)
1√3(→i+→j−→k)
Let ^a=x^i+y^j+z^k⇒∣∣ ∣∣xyz113131∣∣ ∣∣=0⇒4x−y−z=0also x+y+z=0⇒x=0 and y=−z∴^a=y^j−y^k is a unit vector⇒y=1√2∴^a=1√2(^j−^k)