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  • Perplex
    IB Math AIHL
    /
    Matrices
    /

    Eigenvalues & Eigenvectors

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    Exercises

    Key Skills

    Eigenvalues & Eigenvectors

    Eigenvalues & Eigenvectors

    Find eigenvalues & eigenvectors, and using them to diagonalize and find powers of matrices.

    Want a deeper conceptual understanding? Try our interactive lesson!

    Exercises

    No exercises available for this concept.

    Practice exam-style eigenvalues & eigenvectors problems

    Key Skills

    Definition of eigenvectors & eigenvalues
    AHL AI 1.15

    The eigenvectors of a matrix ​A​ are the vector(s) ​v​ such that

    ​
    Av=λv
    ​

    for some constant(s) ​λ​ which we call eigenvalues.

    Finding Eigenvalues
    AHL AI 1.15

    The eigenvalues ​λ​ of a matrix ​A​ satisfy

    ​
    det(A−λI)=0
    ​

    For example, if ​A=(−1−2​34​)​ then

    ​
    det(−1−λ−2​34−λ​)=0⟹(−1−λ)(4−λ)+6=0
    ​

    which simplifies to

    ​
    λ2−3λ+2=0⇒λ=−1,−2
    ​

    We call ​λ2−3λ+2​ the characteristic polynomial of ​A.

    Finding Eigenvectors
    AHL AI 1.15

    If we know an eigenvalue of a matrix ​A, we can find the corresponding eigenvector using its definition:

    ​
    A=(ac​bd​)(xy​)=λ(xy​).
    ​

    When the matrix ​A​ is known, we can solve this system of simultaneous equations to find the eigenvector ​(xy​).

    Diagonalizing a matrix
    AHL AI 1.15

    If a matrix ​A​ has two distinct, real eigenvalues, then we can write it in the form

    ​
    A=PDP−1
    ​

    where ​P=(v1​v2​)​ is formed with the eigenvectors of ​A​ as its columns, and ​D=(λ1​0​0λ2​​)​ is a diagonal matrix.