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Q. Statement 1 : The vectors $\vec{a}$, $\vec{b}$ and $\vec{c}$ lie in the same plane if and only if $\vec{a}. \left(\vec{b}\times\vec{c}\right) = 0$
Statement 2 : The vectors $\vec{u}$ and $\vec{v}$ are perpendicular if and only if $\vec{u} .$$\vec{v}$ = 0 where $\vec{u} \times$$\vec{v}$ is a vector perpendicular to the plane of $\vec{u}$ and $\vec{v}$

AIEEEAIEEE 2012Vector Algebra

Solution:

Statement - 1
The vectors $\vec{a}, \vec{b}$ and $\vec{c}$ lie in the same plane.
$\Rightarrow \vec{a}, \vec{b}$ and $\vec{c}$ are coplanar.
We know, the necessary and sufficient conditions for three vectors to be coplanar is that $\left[\vec{a} \vec{b} \vec{c}\right] = 0$
$i. e. \vec{a}\cdot \left(\vec{b} \times \vec{c}\right) = 0$
Hence, statement-1 is true.