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WAEC Further Mathematics 2016 Question 26

Question 26

Differentiation

Find limx→−3 ((2x2 + x − 21)/(x − 3)).

  1. A.0
  2. B.1
  3. C.7
  4. D.13
Show the answer and explanation

Answer: B (1)

Explanation

Substituting x = −3: (18 − 3 − 21)/(−6) = −6/−6 = 1. (Factorising, 2x² + x − 21 = (2x + 7)(x − 3), so the expression is 2x + 7 = 1 at x = −3.)