Curated prompts

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

  1. Advanced

    Where does a Laplace transform live?

    For f(t)=e2tsin⁡tf(t) = e^{2t}\sin t, find L{f}(s)\mathcal{L}\{f\}(s) and its region of convergence. Why is the formula meaningful outside that region only through analytic continuation?

    A strong contribution: Gives 1/((s−2)2+1)1/((s-2)^2+1) for Re⁡s>2\operatorname{Re} s > 2 and distinguishes the integral from the continued function.

  2. Advanced

    Fourier conventions and where the 2π2\pi goes

    Compute the Fourier transform of e−∣t∣e^{-|t|} under two conventions: ∫f(t)e−iωt dt\int f(t)e^{-i\omega t}\,dt and ∫f(t)e−2πiξt dt\int f(t)e^{-2\pi i \xi t}\,dt. How do the inversion formulas differ?

    A strong contribution: Both transforms computed correctly with the matching inverse formulas stated.

  3. Advanced

    Reading L{sin⁡bx}\mathcal{L}\{\sin bx\} as geometry

    With r=t2+b2r = \sqrt{t^2 + b^2} and θ=arctan⁡(b/t)\theta = \arctan(b/t), check that L{sin⁡bx}(t)=sin⁡θ/r\mathcal{L}\{\sin bx\}(t) = \sin\theta / r. What happens to θ\theta as t→0+t \to 0^+, and what does that say about the transform?

    A strong contribution: Verifies the identity and interprets θ→π/2\theta \to \pi/2, r→br \to b in terms of the limiting value 1/b1/b.

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