A) \[B=0\]
B) \[\vec{A},\vec{B}\] antiparallel
C) \[\vec{A},\vec{B}\] are perpendicular
D) \[\vec{A}.\vec{B}\le 0\]
Correct Answer: B
Solution :
[b] \[(\vec{A}+\vec{B}).(\vec{A}+\vec{B})=\vec{A}.\vec{A}\] \[\Rightarrow \] \[{{A}^{2}}+{{B}^{2}}+2\vec{A}.\vec{B}={{A}^{2}}\] \[\Rightarrow \] \[2\vec{A}.\vec{B}=-{{B}^{2}}\]
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