If the vectors P→=ai^+aj^+3k^  and Q→=ai^−2j^−k^  are perpendicular to each then the value of a  can be :

P→.Q→=0  (If P→  and Q→  are perpendicular to each other) (ai^+aj^+3k^).(ai^−2j^−k^)=0 a.a−a.2−3.1=0 a2−2a−3=0 a2−3a+a−3=0 (a−3)(a+1)=0 a=3  and a=−1