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Find the values of x where the curve y = x\(^3\) + 2x\(^2\) - 5x...

Mathematics
JAMB 2004

Find the values of x where the curve y = x\(^3\) + 2x\(^2\) - 5x - 6 crosses the x - axis.

  • A. -2, -1, and 3
  • B. -2, 1 and -3
  • C. 2, -1, and -3
  • D. 2, 1, and 3
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Correct Answer: Option C
Explanation

To find the values of \( x \) where the curve 

\(y = x^3 + 2x^2 - 5x - 6\)

crosses the x-axis, we set \( y = 0 \):

\(x^3 + 2x^2 - 5x - 6 = 0\)

Testing for rational roots, we find that \( x = -1 \) is a root. Factoring the polynomial gives:

\(x^3 + 2x^2 - 5x - 6 = (x + 1)(x^2 + x - 6)\)

Solving the quadratic \( x^2 + x - 6 = 0 \) using the quadratic formula yields:

\(x = \frac{-1 \pm \sqrt{1^2 - 4 \cdot 1 \cdot -6}}{2 \cdot 1} = \frac{-1 \pm 5}{2}\)

Thus, the solutions are:

\(x = -1, \quad x = 2, \quad x = -3\)

Therefore, the values of \( x \) where the curve crosses the x-axis are  \(x = -1, \quad x = 2, \quad x = -3\).


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JAMB CBT Mobile App 2025 - Free Download
JAMB CBT 2025 - Candidates, Schools, Centres, Resellers - Get Ready!
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WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076
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