A curve is given by \(y = 5 - x - 2x^{2}\). Find the equation of its line of symmetry.

  • A \(x = \frac{-41}{8}\)
  • B \(x = \frac{-1}{4}\)
  • C \(x = \frac{1}{4}\)
  • D \(x = \frac{41}{8}\)
waec 2017furthermathematics

The correct answer is B. \(x = \frac{-1}{4}\)

The line of symmetry of the curve is at the minimum point of the curve (ie y' = 0)

\(\frac{ \mathrm d}{ \mathrm d x} \left ( 5-x-2x^{2} \right)\) = -1 - 4x

If y' = 0, we have \(-1 - 4x = 0 \implies 4x = -1\)

\(x = \frac{-1}{4}\)

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