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Matrices and Determinants question

2022 · Shift 2 · Q34
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  5. /2022 · Shift 2 · Q34

Matrices and Determinants question

2022 · Shift 2 · Q34

JEE AdvancedMathematicsMatrices and DeterminantsMCQ+3 / −1
If M=(5232−32−12)M=\left(\begin{array}{rr}\frac{5}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{1}{2}\end{array}\right)M=(25​−23​​23​−21​​), then which of the following matrices is equal to M2022?M^{2022} ?M2022?
  1. A
    (30343033−3033−3032)\left(\begin{array}{rr}3034 & 3033 \\ -3033 & -3032\end{array}\right)(3034−3033​3033−3032​)
  2. B
    (3034−30333033−3032)\left(\begin{array}{ll}3034 & -3033 \\ 3033 & -3032\end{array}\right)(30343033​−3033−3032​)
  3. C
    (30333032−3032−3031)\left(\begin{array}{rr}3033 & 3032 \\ -3032 & -3031\end{array}\right)(3033−3032​3032−3031​)
  4. D
    (30323031−3031−3030)\left(\begin{array}{rr}3032 & 3031 \\ -3031 & -3030\end{array}\right)(3032−3031​3031−3030​)
View written solutionFree

Correct answer: A

Step-by-Step Solution

  1. Analyze the Matrix and the Problem We are given the matrix M=(5232−32−12)M=\left(\begin{array}{rr}\frac{5}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{1}{2}\end{array}\right)M=(25​−23​​23​−21​​) and asked to compute M2022M^{2022}M2022. Calculating a high power of a matrix suggests using methods like diagonalization or the Cayley-Hamilton theorem.

  2. Find the Characteristic Equation of M The characteristic equation is given by det⁡(M−λI)=0\det(M - \lambda I) = 0det(M−λI)=0. First, let's find the trace and determinant of MMM. Trace, tr(M)=52+(−12)=42=2\text{tr}(M) = \frac{5}{2} + (-\frac{1}{2}) = \frac{4}{2} = 2tr(M)=25​+(−21​)=24​=2. Determinant, det⁡(M)=(52)(−12)−(32)(−32)=−54+94=44=1\det(M) = (\frac{5}{2})(-\frac{1}{2}) - (\frac{3}{2})(-\frac{3}{2}) = -\frac{5}{4} + \frac{9}{4} = \frac{4}{4} = 1det(M)=(25​)(−21​)−(23​)(−23​)=−45​+49​=44​=1.

    The characteristic equation for a 2x2 matrix is λ2−tr(M)λ+det⁡(M)=0\lambda^2 - \text{tr}(M)\lambda + \det(M) = 0λ2−tr(M)λ+det(M)=0. Substituting the values, we get: λ2−2λ+1=0\lambda^2 - 2\lambda + 1 = 0λ2−2λ+1=0 This can be factored as: (λ−1)2=0(\lambda - 1)^2 = 0(λ−1)2=0 The matrix has a repeated eigenvalue λ=1\lambda = 1λ=1.

  3. Apply the Cayley-Hamilton Theorem The Cayley-Hamilton theorem states that a matrix satisfies its own characteristic equation. So, we can replace λ\lambdaλ with MMM: (M−1⋅I)2=O(M - 1 \cdot I)^2 = O(M−1⋅I)2=O (M−I)2=O(M - I)^2 = O(M−I)2=O where III is the identity matrix and OOO is the zero matrix.

  4. Decompose the Matrix M Let's define a new matrix N=M−IN = M - IN=M−I. From the previous step, we have N2=ON^2 = ON2=O. A matrix NNN such that Nk=ON^k = ONk=O for some integer kkk is called a nilpotent matrix. Here, NNN is nilpotent of index 2. We can express MMM as M=I+NM = I + NM=I+N.

  5. Calculate M2022M^{2022}M2022 using Binomial Expansion We want to compute M2022=(I+N)2022M^{2022} = (I + N)^{2022}M2022=(I+N)2022. Since the identity matrix III commutes with any matrix NNN, we can use the binomial theorem: (I+N)2022=(20220)I2022N0+(20221)I2021N1+(20222)I2020N2+⋯+(20222022)N2022(I + N)^{2022} = \binom{2022}{0}I^{2022}N^0 + \binom{2022}{1}I^{2021}N^1 + \binom{2022}{2}I^{2020}N^2 + \dots + \binom{2022}{2022}N^{2022}(I+N)2022=(02022​)I2022N0+(12022​)I2021N1+(22022​)I2020N2+⋯+(20222022​)N2022 Since N2=ON^2 = ON2=O, all terms involving NkN^kNk for k≥2k \ge 2k≥2 will be zero. The expansion simplifies to: M2022=(20220)I+(20221)NM^{2022} = \binom{2022}{0}I + \binom{2022}{1}NM2022=(02022​)I+(12022​)N M2022=1⋅I+2022⋅NM^{2022} = 1 \cdot I + 2022 \cdot NM2022=1⋅I+2022⋅N

  6. Perform the final calculation First, calculate the matrix NNN: N=M−I=(5232−32−12)−(1001)=(3232−32−32)N = M - I = \left(\begin{array}{rr}\frac{5}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{1}{2}\end{array}\right) - \left(\begin{array}{rr}1 & 0 \\ 0 & 1\end{array}\right) = \left(\begin{array}{rr}\frac{3}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{3}{2}\end{array}\right)N=M−I=(25​−23​​23​−21​​)−(10​01​)=(23​−23​​23​−23​​) Now substitute this into the expression for M2022M^{2022}M2022: M2022=I+2022N=(1001)+2022(3232−32−32)M^{2022} = I + 2022N = \left(\begin{array}{rr}1 & 0 \\ 0 & 1\end{array}\right) + 2022 \left(\begin{array}{rr}\frac{3}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{3}{2}\end{array}\right)M2022=I+2022N=(10​01​)+2022(23​−23​​23​−23​​) M2022=(1001)+(2022⋅322022⋅32−2022⋅32−2022⋅32)M^{2022} = \left(\begin{array}{rr}1 & 0 \\ 0 & 1\end{array}\right) + \left(\begin{array}{rr}2022 \cdot \frac{3}{2} & 2022 \cdot \frac{3}{2} \\ -2022 \cdot \frac{3}{2} & -2022 \cdot \frac{3}{2}\end{array}\right)M2022=(10​01​)+(2022⋅23​−2022⋅23​​2022⋅23​−2022⋅23​​) 2022⋅32=1011⋅3=30332022 \cdot \frac{3}{2} = 1011 \cdot 3 = 30332022⋅23​=1011⋅3=3033 M2022=(1001)+(30333033−3033−3033)M^{2022} = \left(\begin{array}{rr}1 & 0 \\ 0 & 1\end{array}\right) + \left(\begin{array}{rr}3033 & 3033 \\ -3033 & -3033\end{array}\right)M2022=(10​01​)+(3033−3033​3033−3033​) M2022=(1+30330+30330−30331−3033)=(30343033−3033−3032)M^{2022} = \left(\begin{array}{cc}1+3033 & 0+3033 \\ 0-3033 & 1-3033\end{array}\right) = \left(\begin{array}{rr}3034 & 3033 \\ -3033 & -3032\end{array}\right)M2022=(1+30330−3033​0+30331−3033​)=(3034−3033​3033−3032​)

  7. Conclusion The calculated matrix M2022M^{2022}M2022 is (30343033−3033−3032)\left(\begin{array}{rr}3034 & 3033 \\ -3033 & -3032\end{array}\right)(3034−3033​3033−3032​). This matches option A.

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