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The value of \(\left(\dfrac{\Delta^{2}}{E}\right) x^{2}\) (taking \(h = 1\)) is :

where :
\(\Delta\) - forward difference operator
E - shift operator.

  • A.-1
  • B.0
  • C.1
  • D.2

Answer: D

The value is 2.

The shift operator acts by \(E f(x) = f(x + h)\), so \(E^{-1}f(x) = f(x - 1)\) with \(h = 1\), and \(\Delta\) commutes with E. Hence

\[ \frac{\Delta^{2}}{E}x^{2} = \Delta^{2}(x - 1)^{2} \]

The second forward difference of any quadratic \(ax^{2} + bx + c\) with step 1 is the constant \(2a\). Here \(a = 1\), so the result is 2, whatever the shift. Directly: \(\Delta x^{2} = 2x + 1\) and \(\Delta(2x + 1) = 2\).

0 would be the third difference of a quadratic, and \(\pm 1\) come from forgetting the factor 2.

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