If the solution set of \(x^{2} + kx - 5 = 0\) is (-1, 5),
FURTHER MATHEMATICS
WAEC 2016
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
Correct Answer: B. -4
Explanation
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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