Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Vectors

Question:

Statement-1: Let $V_1$ be the volume of a parallelopiped ABCDEF having $\vec a,\vec b,\vec c$ as three coterminous edges and $V_2$ be the volume of the parallelopiped PQRSTU having three coterminous edges as vectors whose magnitudes are equal to the areas of three adjacent faces of the parallelopiped ABCDEF. Then, $V_2=2V_1^2$.

Statement-2: For any three vectors $\vec α,\vec β,\vec γ$

$\begin{bmatrix}\vec α×\vec β&\vec β×\vec γ&\vec γ×α\end{bmatrix}=[\vec α\,\,\vec β\,\,\vec γ]^2$

Options:

Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1.

Statement-1 is True, Statement-2 is True; Statement-2 is not a correct explanation for Statement-1.

Statement-1 is True, Statement-2 is False.

Statement-1 is False, Statement-2 is True.

Correct Answer:

Statement-1 is False, Statement-2 is True.

Explanation:

Clearly, statement-2 is true.

Three coterminous edges of parallelopiped PQRSTU are $\vec a×\vec b, \vec b×\vec c$ and $\vec c×\vec a$.

$∴V_2=\left|\begin{bmatrix}\vec a×\vec b&\vec b×\vec c&\vec c×\vec a\end{bmatrix}\right|$

$⇒V_2=\left|[\vec a\,\,\vec b\,\,\vec c]^2\right|$  [Using statement-2]

$⇒V_2=\left|[\vec a\,\,\vec b\,\,\vec c]\right|^2⇒V_2=V_1^2$