Q. $\lbrack\overrightarrow{\mathbf{b}}\mathbf{\times}\overrightarrow{\mathbf{c}}\mathbf{\ \ }\overrightarrow{\mathbf{c}}\mathbf{\times}\overrightarrow{\mathbf{a}}\mathbf{\ \ }\overrightarrow{\mathbf{a}}\mathbf{\times}\overrightarrow{\mathbf{b}}\rbrack$ is equal to

A) [ $\overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\ }\overrightarrow{\mathbf{c}}\mathbf{\ \rbrack}$
B) 2[ $\overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\ }\overrightarrow{\mathbf{c}}\mathbf{\ \rbrack}$
C) $\left\lbrack \mathbf{\ }\overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\ }\overrightarrow{\mathbf{c}}\mathbf{\ } \right\rbrack^{2}$
D) $\overrightarrow{\mathbf{a}}\mathbf{\ }\mathbf{\times (}\overrightarrow{\mathbf{b}}\mathbf{\times}\overrightarrow{\mathbf{c}}\mathbf{)}$
Explanation

(c)
We know, $\lbrack\overrightarrow{\mathbf{b}}\mathbf{\times}\overrightarrow{\mathbf{c}}\mathbf{\ \ }\overrightarrow{\mathbf{c}}\mathbf{\times}\overrightarrow{\mathbf{a}}\mathbf{\ \ }\overrightarrow{\mathbf{a}}\mathbf{\times}\overrightarrow{\mathbf{b}}\rbrack$
$= \left( \mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\times}\overrightarrow{\mathbf{c}} \right)\mathbf{\bullet}\left\lbrack \left( \overrightarrow{\mathbf{c}}\mathbf{\times}\overrightarrow{\mathbf{a}} \right)\mathbf{\bullet}\left( \overrightarrow{\mathbf{a}}\mathbf{\times}\overrightarrow{\mathbf{b}} \right) \right\rbrack$
$= \left( \mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\times}\overrightarrow{\mathbf{c}} \right)\mathbf{\bullet}\left\lbrack \mathbf{\ }\left( \left( \overrightarrow{\mathbf{c}}\mathbf{\times}\overrightarrow{\mathbf{a}} \right)\mathbf{\bullet}\overrightarrow{\mathbf{b}} \right)\overrightarrow{\mathbf{a}}\mathbf{-}\left( \left( \overrightarrow{\mathbf{c}}\mathbf{\times}\overrightarrow{\mathbf{a}} \right)\mathbf{\bullet}\overrightarrow{\mathbf{a}}\mathbf{\ } \right)\overrightarrow{\mathbf{b}}\mathbf{\ } \right\rbrack$
$= \left( \mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\times}\overrightarrow{\mathbf{c}} \right)\mathbf{\bullet}\left( \mathbf{\ }\left\lbrack \mathbf{\ }\overrightarrow{\mathbf{c}}\mathbf{\ }\overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\ } \right\rbrack\overrightarrow{\mathbf{a}}\mathbf{-}\left\lbrack \mathbf{\ }\overrightarrow{\mathbf{c}}\mathbf{\ }\overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{a}}\mathbf{\ } \right\rbrack\mathbf{\ }\overrightarrow{\mathbf{b}} \right)$
$= \left( \mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\times}\overrightarrow{\mathbf{c}} \right)\mathbf{\bullet}\overrightarrow{\mathbf{a}}\left\lbrack \mathbf{\ }\overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\overrightarrow{\mathbf{c}}\mathbf{\ } \right\rbrack - 0$
$= \lbrack\ \overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\ }\overrightarrow{\mathbf{c}}\mathbf{\ \rbrack\lbrack\ }\overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\ }\overrightarrow{\mathbf{c}}\ \rbrack$
$= \left\lbrack \ \overrightarrow{\mathbf{a}}\mathbf{\ }\overrightarrow{\mathbf{b}}\mathbf{\ }\overrightarrow{\mathbf{c}}\ \right\rbrack^{2}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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