If the vectors →a+→b+→c,→a+λ→b+2→c,−→a+→b+→c are linearly dependent then λ=
Let →a,→b,→c be three vectors such that |→a|=|→c|=1;|→b|=4 and |→b×→c|=√15. If →b−2→c=λ→a then a value of λ is