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Which of the following is not correct ?

  • A.\(E = 1 + \Delta\)
  • B.\(\Delta = \nabla(1 - \nabla)^{-1}\)
  • C.\(\nabla = E^{-1}\Delta\)
  • D.\(1 + \Delta = (E + 1)\nabla^{-1}\)

Answer: D

The incorrect relation is \(1 + \Delta = (E + 1)\nabla^{-1}\).

With \(Ef(x) = f(x + h)\), \(\Delta = E - 1\) and \(\nabla = 1 - E^{-1}\):

  • \(E = 1 + \Delta\): true by definition.
  • \(1 - \nabla = E^{-1}\), so \(\nabla(1 - \nabla)^{-1} = \nabla E = E - 1 = \Delta\): true.
  • \(E^{-1}\Delta = E^{-1}(E - 1) = 1 - E^{-1} = \nabla\): true.

But \(\nabla^{-1} = E(E - 1)^{-1}\), so \((E + 1)\nabla^{-1} = E(E + 1)/(E - 1)\), which is not \(1 + \Delta = E\). So option D is the false one.

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