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UI Post-UTME Mathematics 2025 (Model questions) Question 18

Question 18

Polynomials

Find the coefficient of x3 in the expression (2x − 1/x)5

  1. A.40
  2. B.−80
  3. C.80
  4. D.−40
Show the answer and explanation

Answer: B (−80)

Explanation

The general term is ⁵Cᵣ(2x)⁵⁻ʳ(−1/x)ʳ, with power of x = 5 − 2r. For x³, r = 1: 5 × 2⁴ × (−1) = −80.