Question

Let \[\left| {\begin{array}{*{20}{c}} {1 + x}&x&{{x^2}} \\ x&{1 + x}&{{x^2}} \\ {{x^2}}&x&{1 + x} \end{array}} \right| = a{x^5} + b{x^4} + c{x^3} + d{x^2} + \lambda x + \mu \]            be an identity in $$x,$$ where $$a, b, c, d,$$  $$\lambda ,\mu $$  are independent of $$x.$$ Then the value of $$\lambda$$ is

A. 3  
B. 2
C. 4
D. None of these
Answer :   3
Solution :
\[\vartriangle = {\left( {1 + x} \right)^2}\left| {\begin{array}{*{20}{c}} 1&x&{{x^2}} \\ 1&{1 + x}&{{x^2}} \\ 1&x&{1 + x} \end{array}} \right|.\]
Differentiating both sides of the given equality w.r.t. $$x,$$ we get
\[2\left( {1 + x} \right)\left| {\begin{array}{*{20}{c}} 1&x&{{x^2}} \\ 1&{1 + x}&{{x^2}} \\ 1&x&{1 + x} \end{array}} \right| + {\left( {1 + x} \right)^2}\left\{ {\left| {\begin{array}{*{20}{c}} 1&1&{{x^2}} \\ 1&1&{{x^2}} \\ 1&1&{1 + x} \end{array}} \right| + \left| {\begin{array}{*{20}{c}} 1&x&{2x} \\ 1&{1 + x}&{2x} \\ 1&x&1 \end{array}} \right|} \right\} = 5a{x^4} + 4b{x^3} + 3c{x^2} + 2dx + \lambda .\]
Putting $$x = 0,$$
\[2\left| {\begin{array}{*{20}{c}} 1&0&0 \\ 1&1&0 \\ 1&0&1 \end{array}} \right| + \left| {\begin{array}{*{20}{c}} 1&0&0 \\ 1&1&0 \\ 1&0&1 \end{array}} \right| = \lambda \]
\[\therefore \,\,2 + 1 = \lambda .\]

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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