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High Power Evaluation of Two by Two Matrix

If M=(5232−32−12)M = \begin{pmatrix} \frac{5}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{1}{2} \end{pmatrix}, then which of the following matrices is equal to M2022M^{2022} ?

Options

A

(30343033−3033−3032)\begin{pmatrix} 3034 & 3033 \\ -3033 & -3032 \end{pmatrix}

Correct
B

(3034−30333033−3032)\begin{pmatrix} 3034 & -3033 \\ 3033 & -3032 \end{pmatrix}

C

(30333032−3032−3031)\begin{pmatrix} 3033 & 3032 \\ -3032 & -3031 \end{pmatrix}

D

(30323031−3031−3030)\begin{pmatrix} 3032 & 3031 \\ -3031 & -3030 \end{pmatrix}

Topics & Concepts

Step-by-Step Solution

To find the matrix M2022M^{2022}, we first analyze the properties of the given matrix:

M=(5232−32−12)M = \begin{pmatrix} \frac{5}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{1}{2} \end{pmatrix}

Step 1: Compute the trace and determinant of MM

  • tr(M)=52+(−12)=2\text{tr}(M) = \frac{5}{2} + \left(-\frac{1}{2}\right) = 2
  • det⁡(M)=(52)(−12)−(32)(−32)=−54+94=1\det(M) = \left(\frac{5}{2}\right)\left(-\frac{1}{2}\right) - \left(\frac{3}{2}\right)\left(-\frac{3}{2}\right) = -\frac{5}{4} + \frac{9}{4} = 1

Step 2: Find the characteristic equation of MM The characteristic polynomial of MM is given by: λ2−tr(M)λ+det⁡(M)=0\lambda^2 - \text{tr}(M)\lambda + \det(M) = 0 λ2−2λ+1=0  ⟹  (λ−1)2=0\lambda^2 - 2\lambda + 1 = 0 \implies (\lambda - 1)^2 = 0

By the Cayley-Hamilton theorem, every matrix satisfies its own characteristic equation: (M−I)2=0(M - I)^2 = 0

Step 3: Decomposition into an identity matrix and a nilpotent matrix Let N=M−IN = M - I. Then: N=(52−132−32−12−1)=(3232−32−32)N = \begin{pmatrix} \frac{5}{2} - 1 & \frac{3}{2} \\ -\frac{3}{2} & -\frac{1}{2} - 1 \end{pmatrix} = \begin{pmatrix} \frac{3}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{3}{2} \end{pmatrix}

Since (M−I)2=0(M - I)^2 = 0, NN is a nilpotent matrix of index 2, meaning N2=0N^2 = 0.

Step 4: Compute M2022M^{2022} using the binomial theorem Since M=I+NM = I + N and the identity matrix II commutes with NN: Mn=(I+N)n=∑k=0n(nk)In−kNkM^n = (I + N)^n = \sum_{k=0}^n \binom{n}{k} I^{n-k} N^k

Since Nk=0N^k = 0 for all k≥2k \ge 2, the expansion simplifies to: Mn=I+nNM^n = I + nN

Substituting n=2022n = 2022: M2022=I+2022NM^{2022} = I + 2022 N

Step 5: Perform the matrix addition 2022N=2022(3232−32−32)=(30333033−3033−3033)2022 N = 2022 \begin{pmatrix} \frac{3}{2} & \frac{3}{2} \\ -\frac{3}{2} & -\frac{3}{2} \end{pmatrix} = \begin{pmatrix} 3033 & 3033 \\ -3033 & -3033 \end{pmatrix}

Now, adding the identity matrix II: M2022=(1001)+(30333033−3033−3033)=(30343033−3033−3032)M^{2022} = \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix} + \begin{pmatrix} 3033 & 3033 \\ -3033 & -3033 \end{pmatrix} = \begin{pmatrix} 3034 & 3033 \\ -3033 & -3032 \end{pmatrix}

Thus, the correct option is (A).

High Power Evaluation of Two by Two Matrix | Mathematics PYQ Solution - JEE Challenger