Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2020/ii/paper-3/21i/a/solution

For a bounded linear operator , the spectrum is
while the point spectrum is the set of eigenvalues, equivalently the for which is not injective.
A compact operator maps the unit ball to a relatively compact set. A self-adjoint operator satisfies , or for all . A finite-rank operator has finite-dimensional image.

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