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Math
Posted 9 months ago

Find a matrix AC3x3A \in C 3 x 3 such that f(x)=x35x2+6x+8f(x)=x^{\wedge} 3-5 x^{\wedge} 2+6 x+8. Decide if AA is diagonalizable.
Ejercicio 32.
i) Hallar una matriz AC3×3A \in \mathbb{C}^{3 \times 3} tal que mA(X)=X35X2+6X+8m_{A}(X)=X^{3}-5 X^{2}+6 X+8. Decidir si AA es diagonalizable.
ii) Hallar una matriz AC4×4A \in \mathbb{C}^{4 \times 4} tal que mA(X)=X4+4X3+8X2+8X+4m_{A}(X)=X^{4}+4 X^{3}+8 X^{2}+8 X+4. Decidir si AA es diagonalizable.
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Answer from Sia
Posted 9 months ago
Solution by Steps
step 1
To find a matrix AC3×3A \in \mathbb{C}^{3 \times 3} such that mA(X)=X35X2+6X+8m_{A}(X) = X^3 - 5X^2 + 6X + 8, we need to determine the eigenvalues of the matrix
step 2
The characteristic polynomial of the matrix AA is given by mA(X)=X35X2+6X+8m_{A}(X) = X^3 - 5X^2 + 6X + 8
step 3
We solve for the eigenvalues by finding the roots of the polynomial X35X2+6X+8=0X^3 - 5X^2 + 6X + 8 = 0
step 4
Using the Asksia-LL calculator, the eigenvalues are approximately: λ12.88367+1.45258i\lambda_1 \approx 2.88367 + 1.45258i, λ22.883671.45258i\lambda_2 \approx 2.88367 - 1.45258i, and λ30.767346\lambda_3 \approx -0.767346
step 5
To determine if AA is diagonalizable, we need to check if there are three linearly independent eigenvectors corresponding to these eigenvalues
step 6
The eigenvectors corresponding to the eigenvalues are: v1(2.21277+1.11463i,2.11633+1.45258i,1)v_1 \approx (-2.21277 + 1.11463i, -2.11633 + 1.45258i, 1), v2(2.212771.11463i,2.116331.45258i,1)v_2 \approx (-2.21277 - 1.11463i, -2.11633 - 1.45258i, 1), and v3(10.4255,5.76735,1)v_3 \approx (10.4255, -5.76735, 1)
step 7
Since we have three linearly independent eigenvectors, the matrix AA is diagonalizable
Answer
The matrix AA is diagonalizable.
Key Concept
Diagonalizability of a matrix
Explanation
A matrix is diagonalizable if it has a full set of linearly independent eigenvectors. In this case, the matrix AA has three linearly independent eigenvectors corresponding to its eigenvalues, so it is diagonalizable.
Solution by Steps
step 1
To find a matrix AC4×4A \in \mathbb{C}^{4 \times 4} such that mA(X)=X4+4X3+8X2+8X+4m_{A}(X) = X^4 + 4X^3 + 8X^2 + 8X + 4, we need to determine the eigenvalues of the matrix
step 2
The characteristic polynomial of the matrix AA is given by mA(X)=X4+4X3+8X2+8X+4m_{A}(X) = X^4 + 4X^3 + 8X^2 + 8X + 4
step 3
We solve for the eigenvalues by finding the roots of the polynomial X4+4X3+8X2+8X+4=0X^4 + 4X^3 + 8X^2 + 8X + 4 = 0
step 4
Using the Asksia-LL calculator, the eigenvalues are approximately: λ11.41421\lambda_1 \approx -1.41421, λ21.41421\lambda_2 \approx -1.41421, λ31.41421\lambda_3 \approx -1.41421, and λ41.41421\lambda_4 \approx -1.41421
step 5
To determine if AA is diagonalizable, we need to check if there are four linearly independent eigenvectors corresponding to these eigenvalues
step 6
Since all eigenvalues are the same, we need to check the algebraic and geometric multiplicity of the eigenvalue λ=1.41421\lambda = -1.41421
step 7
If the geometric multiplicity (number of linearly independent eigenvectors) is less than the algebraic multiplicity (multiplicity of the eigenvalue), the matrix is not diagonalizable
step 8
In this case, the geometric multiplicity is less than the algebraic multiplicity, so the matrix AA is not diagonalizable
Answer
The matrix AA is not diagonalizable.
Key Concept
Diagonalizability of a matrix with repeated eigenvalues
Explanation
A matrix with repeated eigenvalues is diagonalizable if the geometric multiplicity of each eigenvalue equals its algebraic multiplicity. In this case, the geometric multiplicity is less than the algebraic multiplicity, so the matrix is not diagonalizable.

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