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WAEC Mathematics 1993 Question 12

Question 12

Algebraic Expressions

Factorize 2x2 − 21x + 45

  1. A.(2x − 9)(x − 5)
  2. B.(2x − 15)(x + 3)
  3. C.(2x + 15)(x − 3)
  4. D.(2x − 15)(x − 3)
  5. E.(2x − 9)(x + 5)
Show the answer and explanation

Answer: D ((2x − 15)(x − 3))

Explanation

Find two numbers with product 2 × 45 = 90 and sum −21: −15 and −6. 2x2 − 6x − 15x + 45 = 2x(x − 3) − 15(x − 3) = (2x − 15)(x − 3).