4MA0 Higher January 2013 Paper 4 Q18
18 Solve \(5x^2 + 2x - 4 = 0\)
Give your solutions correct to 3 significant figures.
Show your working clearly.
(3)
| Scheme | Marks |
|---|---|
| \(\dfrac{-2 \pm \sqrt{2^2 - 4 \times 5 \times -4}}{2 \times 5}\) or for this expression with one or more of \(2^2\), \(4 \times 5 \times (-4)\), \(2 \times 5\) or \(2^2 - 4 \times 5 \times (-4)\) evaluated eg \(\dfrac{-2 \pm \sqrt{84}}{10}\) | M1 |
| \(\sqrt{84}\) or \(\sqrt{4 + 80}\) or \(2\sqrt{21}\) or 9.165… | M1 |
| −1.12, 0.717 | A1 |
| (3) |
Notes
M1: for correct substitution (brackets not necessary)
M1: (independent) for correct simplification of discriminant (if evaluated, at least 3sf rounded or truncated)
A1: for values rounding to −1.12 and 0.717 (−1.11651…, 0.71651…)
Award 3 marks if first M1 scored and answer correct.