If the solution set of \(x^{2} + kx - 5 = 0\) is (-1, 5), find the value of k.

  • A -6
  • B -4
  • C 4
  • D 5
waec 2016furthermathematics

The correct answer is B. -4

Given x = (-1, 5) for the equation \(x^{2} + kx - 5 = 0\)

\(x = -1 \implies x + 1 = 0\); \(x = 5 \implies x - 5 = 0\)

\((x + 1)(x - 5) = 0\), expanding,

\(x^{2} - 5x + x - 5 = 0   \therefore  x^{2} - 4x -  5 = 0\)

\(\therefore\) k = -4.

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