MCQ
If the given vectors $( - bc,\,{b^2} + bc,\,{c^2} + bc),$ $({a^2} + ac,\, - ac,\,{c^2} + ac)$ and $({a^2} + ab,\,{b^2} + ab,\, - ab)$ are coplanar, where none of  $a, b $ and $ c $ is zero, then
  • A
    ${a^2} + {b^2} + {c^2} = 1$
  • $bc + ca + ab = 0$
  • C
    $a + b + c = 0$
  • D
    ${a^2} + {b^2} + {c^2} = bc + ca + ab$

Answer

Correct option: B.
$bc + ca + ab = 0$
b
(b) Accordingly, $\left| {\,\begin{array}{*{20}{c}}{ - bc}&{{b^2} + bc}&{{c^2} + bc}\\{{a^2} + ac}&{ - ac}&{{c^2} + ac}\\{{a^2} + ab}&{{b^2} + ab}&{ - ab}\end{array}\,} \right| = 0$

$ \Rightarrow {(ab + bc + ca)^3} = 0 \Rightarrow ab + bc + ca = 0.$

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