WAEC - Further Mathematics (2009 - No. 7)
Which of the following binary operations is not commutative?
\(a * b = \frac{1}{a} + \frac{1}{b}\)
\(a * b = a + b - ab\)
\(a * b = 2a + 2b + ab\)
\(a * b = a - b + ab\)
설명
All other options given are commutative i.e. \(a * b = b * a\), except option D.
\(a * b = a - b + ab\)
\(b * a = b - a + ba\)
\(a - b = -(b - a) \neq b - a\)