Higher November 2017 Paper 2 Q18
18. Use the formula method to solve \(5(x^2 + 2x) = 73\). [4]
| Scheme | Marks | Comments |
|---|---|---|
| \(5x^2 + 10x - 73 = 0\) or \(x^2 + 2x - 14.6 = 0\) | B2 | B1 for \(5x^2 + 10x = 73\) or \(x^2 + 2x = 73/5\) |
| \((x =)\ \dfrac{-10 \pm \sqrt{10^2 - 4\times5\times-73}}{2\times5}\) or \(\dfrac{-2 \pm \sqrt{2^2 - 4\times1\times-14.6}}{2\times1}\) or \((x =)\ \dfrac{-10 \pm \sqrt{1560}}{10}\) or \(\dfrac{-2 \pm \sqrt{62.4}}{2}\) | M1 | Allow 1 slip in substitution, must be correct formula Accept a method of completing the square, with 1 slip for M1 |
| \((x =)\ 2.94968\ldots\) with \(-4.94968\ldots\) or \(\dfrac{-5 \pm \sqrt{390}}{5}\) | A1 | Accept rounded answers from correct working Allow truncated answers provided at least 2d.p. is shown, e.g. 2.94 with \(-4.9(4\ldots)\) or 2.9 with \(-4.94\) |
| (4) |