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Part CCSIR NET June 2024projection-needs-only-the-subspace-finite

Projection needs only the subspace finite

Consider the real vector space equipped with an inner product. Let W be the subspace of V consisting of polynomials of degree at most 2. Let W^⊥ denote the orthogonal complement of W in V. Which of the following statements are true?

  1. A.There exists a polynomial p(x) ∈ W such that x^{4} - p(x) \in W^
  2. B.W^⊥ = {0}
  3. C.W and W^⊥ have the same dimension over
  4. D.W^⊥ is an infinite dimensional vector space over

You have the answer. Trap Analysis is why the other three were written.

Not a worked solution repeated four times — the specific reasoning error each wrong option was built to reward.

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50 are analysed free — try those first.

Related counterexample: A real matrix with all real eigenvalues is orthogonally diagonalisable

More on this topic

The chapter behind this: Inner products, orthogonality and the spectral theorem — free to read

From Inner Product Spaces and FormsGram–Schmidt, orthogonal/unitary/normal matrices, spectral theorem

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