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The binary operation on the set of real numbers is defined by m*n = \(\frac{mn}{2}\)...

Mathematics
JAMB 2012

The binary operation on the set of real numbers is defined by m*n = \(\frac{mn}{2}\) for all m, n \(\in\) R. If the identity element is 2, find the inverse of -5

  • A. \(-\frac{4}{5}\)
  • B. \(-\frac{2}{5}\)
  • C. 4
  • D. 5
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Correct Answer: Option A
Explanation

m * n = \(\frac{mn}{2}\)

Identify, e = 2

Let a \(\in\) R, then

a * a\(^{-1}\) = e

a * a\(^{-1}\) = 2

-5 * a\(^{-1}\) = 2

\(\frac{-5 \times a^{-1}}{2} = 2\)

\(a^{-1} = \frac{2 \times 2}{-5}\)

\(a^{-1} = -\frac{4}{5}\)

There is an explanation video available below.


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Explanation Video

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