\(P = \begin{bmatrix} -1 \\\ -6 \\\ 7\end{bmatrix}, Q = \begin{bmatrix} -9 \\\ -2 \\\ 1 \end{bmatrix} \ \rm and \ R = \begin{bmatrix} 9 \\\ 2 \\\ -1 \end{bmatrix}\) are three vectors.
An orthogonal set of vectors having a span that contains P, Q, R is
1
\(\begin{bmatrix} -5 \\\ -4 \\\ 4 \end{bmatrix} \begin{bmatrix} 4 \\\ -2 \\\ 3 \end{bmatrix}\)
2
\(\begin{bmatrix} 4 \\\ 3 \\\ 4\end{bmatrix} \begin{bmatrix} 1 \\\ 31 \\\ 3 \end{bmatrix} \begin{bmatrix} 5 \\\ 3 \\\ 4 \end{bmatrix}\)
3
\(\begin{bmatrix} 6 \\\ 7 \\\ -1 \end{bmatrix} \begin{bmatrix} -3 \\\ 2 \\\ -6 \end{bmatrix}\)
4
None of the above