Using the three-point inverse DFT, $x[n]=(1/3)\sum_{k=0}^2X[k]e^{j2\pi kn/3}$. For n = 2 and X[k] = 1, the three cube roots of unity sum to zero. Thus x(2) = 0. Equivalently the inverse DFT of a constant spectrum is a unit impulse at n = 0.
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