June 2019 Paper 2 Q16
16 The curve \(\quad y = 2\sqrt{x - a} + 5 \quad\) passes through the point \((1,\ 8)\)
Work out the value of \(a\). [3 marks]
| Answer | Mark | Comments |
|---|---|---|
| \(\dfrac{8 - 5}{2} = \sqrt{1 - a}\) or \(\dfrac{3}{2} = \sqrt{1 - a}\) or \(3^2 = 2^2(1 - a)\) or \(9 = 4(1 - a)\) | M1 | |
| \(1 - a = \left(\dfrac{3}{2}\right)^2\) or \(1 - a = \dfrac{9}{4}\) or \(9 = 4 - 4a\) or \(\dfrac{4 - 9}{4}\) | M1dep | oe equation or calculation eg \(1 - a = \left(\dfrac{8 - 5}{2}\right)^2\) or \(1 - a = 2.25\) or \(\dfrac{9 - 4}{-4}\) implies M2 |
| \(-\dfrac{5}{4}\) or \(-1.25\) or \(-1\dfrac{1}{4}\) | A1 |
Additional guidance
| \(3 = 2\sqrt{1 - a}\) | M0 |
| Allow recovery of missing brackets |