Find the angle between the vectors \(\vec a = 3\hat i - 2\hat j + \;\hat k\;and\;\vec b = \;\hat i - 2\hat j - 3\hat k\) ?
1
\({\cos ^{ - 1}}\left( {\frac{1}{7}} \right)\)
2
\({\cos ^{ - 1}}\left( {\frac{2}{7}} \right)\)
3
\({\cos ^{ - 1}}\left( {\frac{3}{7}} \right)\)
4
\({\cos ^{ - 1}}\left( {\frac{5}{7}} \right)\)