June 2017 Paper 1 Q2
2 A curve has equation \(\quad y = ax^2 + 3x \quad\) where \(a\) is a constant.
When \(x = -1\), the gradient of the curve is \(-5\)
Work out the value of \(a\). [3 marks]
| Answer | Mark | Comments |
|---|---|---|
| \(2ax\) or \(+3\) | M1 | either term correct |
| their \(2a(-1) + 3 = -5\) | M1dep | oe two terms needed here ... an \(x\) term with \(-1\) substituted and a constant term |
| (\(a\) =) 4 | A1 |
Additional guidance
If \(\mathrm{d}y/\mathrm{d}x = 5\) is used (misread) then \(-2a + 3 = 5\) scores M1 M1 A0
A 1st line of \(2a + 3\) followed by \(2a + 3 = -5\) can only score M1 M0 A0
Condone \(y = 2ax + 3\) for the 1st M1 ... they have differentiated but used the wrong notatioin