Curated prompts

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Written by RIDA MATH. Each prompt says what a strong contribution looks like.

  1. University

    The matrix of d/dxd/dx

    Write the matrix of differentiation on the space spanned by {1,x,x2,x3}\{1, x, x^2, x^3\}. Why is it nilpotent? What is its matrix on {sin⁡x,cos⁡x}\{\sin x, \cos x\}, and what are its eigenvalues?

    A strong contribution: Both matrices written with a stated coordinate convention; nilpotency and eigenvalues ±i\pm i explained.

  2. University

    Which spaces are closed under differentiation?

    Decide whether each span is closed under d/dxd/dx: {ex,xex}\{e^x, xe^x\}, {sin⁡x,x}\{\sin x, x\}, {1/x}\{1/x\}, {sin⁡xcos⁡x,cos⁡2x}\{\sin x \cos x, \cos 2x\}. For the closed ones, give the matrix.

    A strong contribution: Each case justified; the closed cases include a matrix with an explicit basis order.

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