A) \[\text{9}0{}^\circ \]
B) \[0{}^\circ \]
C) \[\text{6}0{}^\circ \]
D) \[\text{45}{}^\circ \]
Correct Answer: A
Solution :
\[\cos \theta =\frac{\overrightarrow{A}.\overrightarrow{B}}{|A||B|}=\frac{(3\hat{i}+4\hat{j}+5\hat{k})\,(3\hat{i}+4\hat{j}-5\hat{k})}{\sqrt{9+16+25}\sqrt{9+16+25}}\] \[=\frac{9+16-25}{50}=0\] Þ \[\cos \theta =0\], \[\therefore \] \[\theta =90{}^\circ \]
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