MCQ
If  $ a, b, c, d$  are coplanar vectors, then $(a \times b) \times (c \times d) = $
  • A
    $|\,a\, \times \,c{|^2}$
  • B
    $|a \times d{|^2}$
  • C
    $|b \times c{|^2}$
  • $0$

Answer

Correct option: D.
$0$
d
(d) $(a \times b) \times (c \times d) = [a\,b\,d]c - [a\,b\,c]d$

$\because a,b,c,d$ are coplanar vectors

$\therefore \,\,\,[a\,b\,d] = [a\,b\,c] = 0.$ So, $(a \times b) \times (c \times d) = 0$.

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