jee-advanced 2018 Q13
3 marks
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Consider the cube in the first octant with sides $O P , O Q$ and $O R$ of length 1 , along the $x$-axis, $y$-axis and $z$-axis, respectively, where $O ( 0,0,0 )$ is the origin. Let $S \left( \frac { 1 } { 2 } , \frac { 1 } { 2 } , \frac { 1 } { 2 } \right)$ be the centre of the cube and $T$ be the vertex of the cube opposite to the origin $O$ such that $S$ lies on the diagonal $O T$. If $\vec { p } = \overrightarrow { S P } , \vec { q } = \overrightarrow { S Q } , \vec { r } = \overrightarrow { S R }$ and $\vec { t } = \overrightarrow { S T }$, then the value of $| ( \vec { p } \times \vec { q } ) \times ( \vec { r } \times \vec { t } ) |$ is $\_\_\_\_$ .