Question
If \[\left| \begin{array}{l}
a\,\,\,\,{a^2}\,\,\,\,\,1 + {a^3}\\
b\,\,\,\,{b^2}\,\,\,\,\,1 + {b^3}\\
c\,\,\,\,\,{c^2}\,\,\,\,\,1 + {c^3}
\end{array} \right| = 0\] and vectors $$\left( {1,\,a,{a^2}} \right),\,\left( {1,\,b,{b^2}} \right)$$ and $$\left( {1,\,c,{c^2}} \right)$$ are non-coplanar, then the product $$abc$$ equals :
A.
$$0$$
B.
$$2$$
C.
$$ - 1$$
D.
$$1$$
Answer :
$$ - 1$$
Solution :
\[\begin{array}{l}
\left| \begin{array}{l}
a\,\,\,\,\,{a^2}\,\,\,\,\,1 + {a^3}\\
b\,\,\,\,\,{b^2}\,\,\,\,\,1 + {b^3}\\
c\,\,\,\,\,{c^2}\,\,\,\,\,1 + {c^3}
\end{array} \right| = 0\\
\Rightarrow \left| \begin{array}{l}
a\,\,\,\,{a^2}\,\,\,\,\,1\\
b\,\,\,\,{b^2}\,\,\,\,\,1\\
c\,\,\,\,\,{c^2}\,\,\,\,\,1
\end{array} \right| + \left| \begin{array}{l}
a\,\,\,\,{a^2}\,\,\,\,\,{a^3}\\
b\,\,\,\,{b^2}\,\,\,\,\,{b^3}\\
c\,\,\,\,\,{c^2}\,\,\,\,\,{c^3}
\end{array} \right| = 0\\
\Rightarrow \left( {1 + abc} \right)\left| \begin{array}{l}
1\,\,\,\,\,a\,\,\,\,{a^2}\\
1\,\,\,\,\,b\,\,\,\,{b^2}\\
1\,\,\,\,\,c\,\,\,\,\,{c^2}
\end{array} \right| = 0\\
{\rm{As }}\left| \begin{array}{l}
1\,\,\,\,\,a\,\,\,\,{a^2}\\
1\,\,\,\,\,b\,\,\,\,{b^2}\\
1\,\,\,\,\,c\,\,\,\,\,{c^2}
\end{array} \right| \ne 0\,\,\,\,\left( {{\rm{given \,\,condition}}} \right)\\
\therefore \,\,abc = - 1
\end{array}\]