June 2018 Paper 1 Q8
8 Write \(\quad (1 + 2\sqrt{5})(4 - \sqrt{5}) \quad\) in the form \(\quad a + b\sqrt{5} \quad\) where \(a\) and \(b\) are integers. [2 marks]
| Answer | Mark | Comments |
|---|---|---|
| \(4 - \sqrt{5} + 8\sqrt{5} - 2\sqrt{5}\,\sqrt{5}\) | M1 | oe allow one incorrect term in a four term expansion |
| \(-6 + 7\sqrt{5}\) | A1 |
Additional guidance
| Any incorrect further work loses the A mark, so they can only score M1 A0 |