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Solve the equation \( 3x^2 − 4x − 5 = 0 \)

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Mathematics JAMB 2015

Solve the equation \( 3x^2 − 4x − 5 = 0 \)

  • x = 1.75 or − 0.15
  • x = 2.12 or − 0.79 checkmark
  • x = 1.5 or − 0.34
  • x = 2.35 or −1.23

The correct answer is: B

Explanation

Using the quadratic formula, we have

\(x = \frac{-b \pm \sqrt{b^{2} - 4ac}}{2a}\)

From the equation \(3x^{2} - 4x - 5 = 0\), a = 3, b = -4 and c = -5.

\(\therefore x = \frac{-(-4) \pm \sqrt{(-4)^{2} - 4(3)(-5)}}{2(3)}\)

= \(\frac{4 \pm \sqrt{16 + 60}}{6}\)

= \(\frac{4 \pm \sqrt{76}}{6}\)

= \(\frac{4 \pm 8.72}{6}\)

= \(\frac{4 + 8.72}{6} \text{ or } \frac{4 - 8.72}{6}\)

= \(\frac{12.72}{6} \text{ or } \frac{-4.72}{6}\)

\(x = \text{2.12 or -0.79}\)

There is an explanation video available .

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