MCQ
If $ a $ and  $b$ are two vectors, then ${(a \times b)^2}$ equals
  • A
    $\left| {\,\begin{array}{*{20}{c}}{a\,\,.\,\,b}&{a\,\,.\,\,a}\\{b\,\,.\,\,b}&{b\,\,.\,\,a}\end{array}\,} \right|$
  • $\left| {\,\begin{array}{*{20}{c}}{a\,\,.\,\,a}&{a\,\,.\,\,b}\\{b\,\,.\,\,a}&{b\,\,.\,\,b}\end{array}\,} \right|$
  • C
    $\left| {\,\begin{array}{*{20}{c}}{a\,\,.\,\,b}\\{b\,\,.\,\,a}\end{array}\,} \right|$
  • D
    None of these

Answer

Correct option: B.
$\left| {\,\begin{array}{*{20}{c}}{a\,\,.\,\,a}&{a\,\,.\,\,b}\\{b\,\,.\,\,a}&{b\,\,.\,\,b}\end{array}\,} \right|$
b
(b) ${(a \times b)^2} = {a^2}{b^2} - {(a\,.\,b)^2} = \left| {\,\begin{array}{*{20}{c}}{a\,.\,a}&{a\,.\,b}\\{a\,.\,b}&{b\,.\,b}\end{array}\,} \right|.$

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