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Solve the inequality \(x^{2} - 2x \geq 3\)

Further Mathematics
WAEC 2012

Solve the inequality \(x^{2} - 2x \geq 3\)

  • A. \(-1 \leq x \leq 3\)
  • B. \(x \geq 3\) and \(x \leq -1\)
  • C. \(x \geq 3\) or \(x < -1\)
  • D. \(-1 \leq x < 3\)
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Correct Answer: Option B
Explanation

\(x^{2} - 2x \geq 3 \implies x^{2} - 2x - 3 \geq 0\)

\(x^{2} + x - 3x - 3 = (x + 1)(x - 3) \geq 0\) 

\(x = -1 ; x = 3\)

Check: \(x = -1  : (-1)^{2} - 2(-1)  = 1 + 2 \geq 3\)  (satisfied)

\(-1 < x < 3 : 0^{2} - 2(0) = 0 \geq 3\) (not satisfied)

\(x < -1 : (-2)^{2} - 2(-2) = 4 + 4 = 8 \geq 3\) (satisfied)

\(x = 3 : 3^{2} - 2(3) = 9 - 6 = 3 \geq 3\) (satisfied)

\(x > 3 : 4^{2} - 2(4) = 16 - 8 = 8 \geq 3\) (satisfied)

\(\therefore x^{2} - 2x \geq \text{3 is satisfied in the region x} \leq \text{-1 and x} \geq 3\) 


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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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WAEC and NECO CBT App for Mobile Devices - Candidates, Schools, Centres, Resellers - 100% Offline -Download Now
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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
Post UTME Past Questions Agent