Q. $\overrightarrow{\mathbf{A}}\ ,\ \overrightarrow{\mathbf{B}}\ ,\ \overrightarrow{\mathbf{C\ }}$ are three non-zero vectors, no two of them are parallel. If $\overrightarrow{\mathbf{A}} + \overrightarrow{\mathbf{B}}$ is collinear to $\overrightarrow{\mathbf{C\ }}\ and\ \overrightarrow{\mathbf{B}} + \overrightarrow{\mathbf{C\ }}\$is collinear to $\overrightarrow{\mathbf{A\ }} + \overrightarrow{\mathbf{B}} + \overrightarrow{\mathbf{C\ }}$ is equal to

A) $\overrightarrow{\mathbf{A}}\$
B) $\overrightarrow{\mathbf{B}}\$
C) $\overrightarrow{\mathbf{C\ }}$
D) $\overrightarrow{\mathbf{0}}$
Explanation

(d)
Since, $\overrightarrow{\mathbf{A}} + \overrightarrow{\mathbf{B}}\$is collinear to $\overrightarrow{\mathbf{C}}$ and $\overrightarrow{\mathbf{B}} + \overrightarrow{\mathbf{C}}$ is collinear to $\overrightarrow{\mathbf{A}}$
$\therefore\ \overrightarrow{\mathbf{A}} + \overrightarrow{\mathbf{B}} = \lambda\ \overrightarrow{\mathbf{C}}\ and\ \overrightarrow{\mathbf{B}} + \overrightarrow{\mathbf{C}} = \mu\ \overrightarrow{\mathbf{A}}$
Where λ and $\mu$ are scalars.
$\Longrightarrow \ \overrightarrow{\mathbf{A}} + \overrightarrow{\mathbf{B}} + \overrightarrow{\mathbf{C}} = (\lambda + 1)\overrightarrow{\mathbf{C}}$
and $\overrightarrow{\mathbf{A}} + \overrightarrow{\mathbf{B}} + \overrightarrow{\mathbf{C}} = (\mu + 1)\overrightarrow{\mathbf{A}}$
$\Longrightarrow (\lambda + 1)\overrightarrow{\mathbf{C}} = (\mu + 1)\overrightarrow{\mathbf{A}}$
If λ$\neq - 1$, then
$\overrightarrow{\mathbf{C}} = \frac{\mu + 1}{\lambda + 1}\overrightarrow{\mathbf{A}}$
⟹ $\overrightarrow{\mathbf{C}}\ and\ \overrightarrow{\mathbf{A}}\$are collinear.
This is a contradiction to the given condition.
$\therefore\ \ \lambda = - 1$
$\therefore\ \ \overrightarrow{\mathbf{A}} + \overrightarrow{\mathbf{B}} + \overrightarrow{\mathbf{C}} = \overrightarrow{\mathbf{0}}$

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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