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Which of the following binary operations is not commutative?

Which of the following binary operations is not commutative?
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  • A \(a * b = \frac{1}{a} + \frac{1}{b}\)
  • B \(a * b = a + b - ab\)
  • C \(a * b = 2a + 2b + ab\)
  • D \(a * b = a - b + ab\)
Correct Answer: Option D
Explanation:
All other options given are commutative i.e. \(a * b = b * a\), except option D.
\(a * b = a - b + ab\)
\(b * a = b - a + ba\)
\(a - b = -(b - a) \neq b - a\)

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