Question

Let $${S_k} = {\alpha ^k} + {\beta ^k} + {\gamma ^k},$$    then \[\Delta = \left| {\begin{array}{*{20}{c}} {{S_0}}&{{S_1}}&{{S_2}}\\ {{S_1}}&{{S_2}}&{{S_3}}\\ {{S_2}}&{{S_3}}&{{S_4}} \end{array}} \right|\]    is equal to

A. $$S_6$$
B. $$S_5 - S_3$$
C. $$S_6 - S_4$$
D. None  
Answer :   None
Solution :
\[\begin{array}{l} \Delta = \left| {\begin{array}{*{20}{c}} {{S_0}}&{{S_1}}&{{S_2}}\\ {{S_1}}&{{S_2}}&{{S_3}}\\ {{S_2}}&{{S_3}}&{{S_4}} \end{array}} \right|\\ = \,\left| {\begin{array}{*{20}{c}} {1 + 1 + 1}&{\alpha + \beta + \gamma }&{{\alpha ^2} + {\beta ^2} + {\gamma ^2}}\\ {\alpha + \beta + \gamma }&{{\alpha ^2} + {\beta ^2} + {\gamma ^2}}&{{\alpha ^3} + {\beta ^3} + {\gamma ^3}}\\ {{\alpha ^2} + {\beta ^2} + {\gamma ^2}}&{{\alpha ^3} + {\beta ^3} + {\gamma ^3}}&{{\alpha ^4} + {\beta ^4} + {\gamma ^4}} \end{array}} \right| \end{array}\]
The above determinant can be expressed as product of two determinants. Thus,
\[\Delta = \left| {\begin{array}{*{20}{c}} 1&1&1\\ \alpha &\beta &\gamma \\ {{\alpha ^2}}&{{\beta ^2}}&{{\gamma ^2}} \end{array}} \right|\,\left| {\begin{array}{*{20}{c}} 1&1&1\\ \alpha &\beta &\gamma \\ {{\alpha ^2}}&{{\beta ^2}}&{{\gamma ^2}} \end{array}} \right| = {\left[ {\left( {\beta - \alpha } \right)\left( {\gamma - \alpha } \right)\left( {\gamma - \beta } \right)} \right]^2}\]

Releted MCQ Question on
Algebra >> Matrices and Determinants

Releted Question 1

Consider the set $$A$$ of all determinants of order 3 with entries 0 or 1 only. Let $$B$$  be the subset of $$A$$ consisting of all determinants with value 1. Let $$C$$  be the subset of $$A$$ consisting of all determinants with value $$- 1.$$ Then

A. $$C$$ is empty
B. $$B$$  has as many elements as $$C$$
C. $$A = B \cup C$$
D. $$B$$  has twice as many elements as elements as $$C$$
Releted Question 2

If $$\omega \left( { \ne 1} \right)$$  is a cube root of unity, then
\[\left| {\begin{array}{*{20}{c}} 1&{1 + i + {\omega ^2}}&{{\omega ^2}}\\ {1 - i}&{ - 1}&{{\omega ^2} - 1}\\ { - i}&{ - i + \omega - 1}&{ - 1} \end{array}} \right|=\]

A. 0
B. 1
C. $$i$$
D. $$\omega $$
Releted Question 3

Let $$a, b, c$$  be the real numbers. Then following system of equations in $$x, y$$  and $$z$$
$$\frac{{{x^2}}}{{{a^2}}} + \frac{{{y^2}}}{{{b^2}}} - \frac{{{z^2}}}{{{c^2}}} = 1,$$    $$\frac{{{x^2}}}{{{a^2}}} - \frac{{{y^2}}}{{{b^2}}} + \frac{{{z^2}}}{{{c^2}}} = 1,$$    $$ - \frac{{{x^2}}}{{{a^2}}} + \frac{{{y^2}}}{{{b^2}}} + \frac{{{z^2}}}{{{c^2}}} = 1$$     has

A. no solution
B. unique solution
C. infinitely many solutions
D. finitely many solutions
Releted Question 4

If $$A$$ and $$B$$ are square matrices of equal degree, then which one is correct among the followings?

A. $$A + B = B + A$$
B. $$A + B = A - B$$
C. $$A - B = B - A$$
D. $$AB=BA$$

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Matrices and Determinants


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