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JAMB Mathematics 1983 Question 10

Question 10

Polynomials

If x + 2 and x − 1 are factors of the expressions lx3 + 2kx2 + 24, find the values of l and k.

  1. A.l = −6, k = −9
  2. B.l = −2, k = 1
  3. C.l = −2, k = −1
  4. D.l = 0, k = 1
  5. E.l = 6, k = 0.
Show the answer and explanation

Answer: A (l = −6, k = −9)

Explanation

Putting x = −2 gives −8l + 8k + 24 = 0, i.e. k − l = −3. Putting x = 1 gives l + 2k + 24 = 0. Solving: k = −9 and l = −6.