MCQ
Given three arbitrary vectors $\bar{a}, \bar{b}, \bar{c}$, the vectors $\bar{\alpha}=5 \overline{ a }+6 \overline{b}+7 \overline{ c }, \beta=7 \overline{ a }-8 \overline{b}+9 \overline{ c }$, $\bar{\gamma}=3 \overline{ a }+20 \overline{b}+5 \overline{ c }$ are
  • A
    Collinear
  • Coplanar
  • C
    Non-coplanar
  • D
    None of these

Answer

Correct option: B.
Coplanar
(B) $[\bar{\alpha} \bar{\beta} \bar{\gamma}]=\left|\begin{array}{ccc}5 & 6 & 7 \\ 7 & -8 & 9 \\ 3 & 20 & 5\end{array}\right|$
$=5(-40-180)-6(35-27)$ $+7(140+24)=0$
∴ the given vectors are coplanar.

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