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 :
\[\begin{array}{l} \left| \begin{array}{l} a\,\,\,\,\,{a^2}\,\,\,\,\,1 + {a^3}\\ b\,\,\,\,\,{b^2}\,\,\,\,\,1 + {b^3}\\ c\,\,\,\,\,{c^2}\,\,\,\,\,1 + {c^3} \end{array} \right| = 0\\ \Rightarrow \left| \begin{array}{l} a\,\,\,\,{a^2}\,\,\,\,\,1\\ b\,\,\,\,{b^2}\,\,\,\,\,1\\ c\,\,\,\,\,{c^2}\,\,\,\,\,1 \end{array} \right| + \left| \begin{array}{l} a\,\,\,\,{a^2}\,\,\,\,\,{a^3}\\ b\,\,\,\,{b^2}\,\,\,\,\,{b^3}\\ c\,\,\,\,\,{c^2}\,\,\,\,\,{c^3} \end{array} \right| = 0\\ \Rightarrow \left( {1 + abc} \right)\left| \begin{array}{l} 1\,\,\,\,\,a\,\,\,\,{a^2}\\ 1\,\,\,\,\,b\,\,\,\,{b^2}\\ 1\,\,\,\,\,c\,\,\,\,\,{c^2} \end{array} \right| = 0\\ {\rm{As }}\left| \begin{array}{l} 1\,\,\,\,\,a\,\,\,\,{a^2}\\ 1\,\,\,\,\,b\,\,\,\,{b^2}\\ 1\,\,\,\,\,c\,\,\,\,\,{c^2} \end{array} \right| \ne 0\,\,\,\,\left( {{\rm{given \,\,condition}}} \right)\\ \therefore \,\,abc = - 1 \end{array}\]

Releted MCQ Question on
Geometry >> 3D Geometry and Vectors

Releted Question 1

The scalar $$\vec A.\left( {\vec B + \vec C} \right) \times \left( {\vec A + \vec B + \vec C} \right)$$      equals :

A. $$0$$
B. $$\left[ {\vec A\,\vec B\,\vec C} \right] + \left[ {\vec B\,\vec C\,\vec A} \right]$$
C. $$\left[ {\vec A\,\vec B\,\vec C} \right]$$
D. None of these
Releted Question 2

For non-zero vectors $$\vec a,\,\vec b,\,\vec c,\,\left| {\left( {\vec a \times \vec b} \right).\vec c} \right| = \left| {\vec a} \right|\left| {\vec b} \right|\left| {\vec c} \right|$$       holds if and only if -

A. $$\vec a.\vec b = 0,\,\,\,\vec b.\vec c = 0$$
B. $$\vec b.\vec c = 0,\,\,\,\vec c.\vec a = 0$$
C. $$\vec c.\vec a = 0,\,\,\,\vec a.\vec b = 0$$
D. $$\vec a.\vec b = \vec b.\vec c = \vec c.\vec a = 0$$
Releted Question 3

The volume of the parallelepiped whose sides are given by $$\overrightarrow {OA} = 2i - 2j,\,\,\overrightarrow {OB} = i + j - k,\,\,\overrightarrow {OC} = 3i - k,$$         is :

A. $$\frac{4}{{13}}$$
B. $$4$$
C. $$\frac{2}{7}$$
D. none of these
Releted Question 4

The points with position vectors $$60i + 3j,\,\,40i - 8j,\,\,ai - 52j$$      are collinear if :

A. $$a = - 40$$
B. $$a = 40$$
C. $$a = 20$$
D. none of these

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