JAMB 2024 Mathematics · Question 49

A binary operation * is defined on a set of real numbers by x*y = xy^y for all values of x and y, if x * 2 = x, find the possible values of x.

Options

  1. A.0, 2
  2. B.1, 2
  3. C.0, 1
  4. D.2, 2

Answer: C. 0, 1

Explanation written with AI and checked against the answer key

Analysis

The problem defines a binary operation x∗y=xyx * y = x^y. We are given the condition x∗2=xx * 2 = x and asked to find the possible values of xx that satisfy this equation.

Concept

A binary operation is simply a rule for combining two numbers. In this case, the rule is to raise the first number to the power of the second number. To solve for xx, we substitute the given values into the defined operation and solve the resulting algebraic equation.

Step-by-Step Solution
  1. Apply the definition: Given x∗y=xyx * y = x^y, substitute y=2y = 2 into the expression: x∗2=x2x * 2 = x^2
  1. Set up the equation: We are told that x∗2=xx * 2 = x. Therefore: x2=xx^2 = x
  1. Solve for xx: Bring all terms to one side to form a quadratic equation: x2−x=0x^2 - x = 0
  1. Factorize the equation: Factor out xx: x(x−1)=0x(x - 1) = 0
  1. Find the roots: For the product to be zero, either: x=0x = 0 or x−1=0  ⟹  x=1x - 1 = 0 \implies x = 1

The possible values for xx are 00 and 11.

Conclusion

Comparing our result with the provided options, we see that 00 and 11 correspond to option C.

Exam Tip

When you have an equation like x2=xx^2 = x, never divide both sides by xx to get x=1x = 1. If you do that, you lose the solution x=0x = 0. Always move all terms to one side and factorize to ensure you capture all possible roots!

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