A) \[\pi \]
B) \[\pi /3\]
C) \[\pi /2\]
D) \[\pi /4\]
Correct Answer: A
Solution :
| [a] Given, \[(A\times B)=(B\times A)\] |
| \[\Rightarrow \]\[(A\times B)-(B\times A)=0\] |
| or \[(A\times B)+(A\times B)=0\] |
| \[[\because (B\times A)=-(A\times B)]\] |
| \[\Rightarrow \]\[2(A\times B)=0\] |
| \[\Rightarrow \]\[2AB\sin \theta =0\] |
| \[\Rightarrow \]\[\sin \theta =0\] |
| \[(\because |A|=A\ne 0,|B|=B\ne 0)\] |
| \[\therefore \] \[\theta =0\]or \[\pi \] |
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