Let $Π_1$ and $Π_2$ be two planes determined by the pairs of vectors $\vec a,\vec b$ and $\vec c,\vec d$ respectively. If the planes $Π_1$ and $Π_2$ are parallel, then
Answer & explanation
Correct answer: option 4
Two planes are parallel, if their normals are parallel.
$∴Π_1$ and $Π_2$ are parallel
$⇒\vec a×\vec b$ and $\vec c×\vec d$ are parallel
$⇒(\vec a×\vec b)×(\vec c×\vec d) =\vec 0$