Math Problem Statement

Let A be a 3 x 3 matrix. Suppose that A has eigenvalues 2 and 1, and suppose that u and v are eigenvectors corresponding to 2 and 1, respectively. Compute A^5w, where w is a vector provided.

Solution

We are given the following information:

  • AA is a 3×33 \times 3 matrix with eigenvalues 2 and 1.
  • u=[101]u = \begin{bmatrix} 1 \\ 0 \\ -1 \end{bmatrix} is an eigenvector corresponding to eigenvalue 2.
  • v=[210]v = \begin{bmatrix} 2 \\ 1 \\ 0 \end{bmatrix} is an eigenvector corresponding to eigenvalue 1.
  • w=[723]w = \begin{bmatrix} 7 \\ 2 \\ -3 \end{bmatrix}.
  • We are tasked with computing A5wA^5 w.

Step 1: Diagonalization Insight

Since AA has distinct eigenvalues and corresponding eigenvectors, it can be diagonalized, meaning: A=PDP1A = PDP^{-1} where DD is a diagonal matrix containing the eigenvalues, and PP is a matrix whose columns are the eigenvectors uu, vv, etc. But we don’t need to explicitly construct AA. Instead, we can take advantage of the following property:

Akv=λkvA^k v = \lambda^k v for any eigenvector vv corresponding to the eigenvalue λ\lambda, where AkA^k is a matrix raised to the power kk.

Step 2: Decomposition of ww

We need to express ww as a linear combination of the eigenvectors uu and vv. Let’s assume: w=c1u+c2vw = c_1 u + c_2 v where c1c_1 and c2c_2 are scalars we need to solve for.

This means: [723]=c1[101]+c2[210]\begin{bmatrix} 7 \\ 2 \\ -3 \end{bmatrix} = c_1 \begin{bmatrix} 1 \\ 0 \\ -1 \end{bmatrix} + c_2 \begin{bmatrix} 2 \\ 1 \\ 0 \end{bmatrix} We now solve for c1c_1 and c2c_2.

Step 3: Solve for c1c_1 and c2c_2

By comparing each component, we can set up a system of equations:

  1. c1+2c2=7c_1 + 2c_2 = 7
  2. c2=2c_2 = 2
  3. c1=3-c_1 = -3

From equation (3), we immediately get c1=3c_1 = 3.

Now substitute c2=2c_2 = 2 and c1=3c_1 = 3 into equation (1): 3+2(2)=73 + 2(2) = 7 This is true, so the solution is c1=3c_1 = 3 and c2=2c_2 = 2.

Thus: w=3u+2vw = 3u + 2v

Step 4: Compute A5wA^5 w

Now that we know w=3u+2vw = 3u + 2v, we can use the eigenvalue property to compute A5wA^5 w.

Since Au=2uA u = 2u and Av=vA v = v, we have: A5u=25u=32uA^5 u = 2^5 u = 32u A5v=15v=vA^5 v = 1^5 v = v

Thus: A5w=A5(3u+2v)=3A5u+2A5v=3(32u)+2v=96u+2vA^5 w = A^5 (3u + 2v) = 3A^5 u + 2A^5 v = 3(32u) + 2v = 96u + 2v

Step 5: Substitute uu and vv

Now substitute the values of uu and vv:

= \begin{bmatrix} 96 \\ 0 \\ -96 \end{bmatrix} + \begin{bmatrix} 4 \\ 2 \\ 0 \end{bmatrix} = \begin{bmatrix} 100 \\ 2 \\ -96 \end{bmatrix}$$ Thus, the result is: $$A^5 w = \begin{bmatrix} 100 \\ 2 \\ -96 \end{bmatrix}$$ Would you like further details or have any questions? Here are 5 related questions you might find interesting: 1. How can you generalize this method to compute $$A^k w$$ for any $$k$$? 2. How would you compute $$A^5$$ if $$A$$ was not diagonalizable? 3. What are the conditions under which a matrix is diagonalizable? 4. Can a matrix with repeated eigenvalues be diagonalizable? 5. How can you find eigenvalues and eigenvectors of larger matrices? **Tip:** Eigenvalues and eigenvectors provide a powerful tool to simplify matrix operations, especially for large powers of matrices. Always check for diagonalizability to ease computations.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Linear Algebra
Eigenvalues
Eigenvectors
Matrix Powers

Formulas

A^k v = λ^k v
w = c1 * u + c2 * v
A^5w = A^5(c1 * u + c2 * v) = c1 * A^5u + c2 * A^5v

Theorems

Eigenvalue and Eigenvector Theorem
Diagonalization of Matrices

Suitable Grade Level

University Level (Linear Algebra Course)