A) \[135{}^\circ \]
B) \[90{}^\circ \]
C) \[{{\cos }^{-1}}\left( \frac{2}{3} \right)\]
D) \[{{\cos }^{-1}}\left( \frac{5}{7} \right)\]
E) \[105{}^\circ \]
Correct Answer: B
Solution :
\[\because \] \[\overset{\to }{\mathop{AB}}\,=4\hat{j}-2\hat{k}\] \[\overset{\to }{\mathop{BC}}\,=\hat{i}-2\hat{j}+6\hat{k}\] and \[\overset{\to }{\mathop{CA}}\,=-\hat{i}-2\hat{j}-4\hat{k}\] \[\Rightarrow \]\[\Delta ABC\]is right angled triangle. \[\therefore \] Greatest angle is\[90{}^\circ \].
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