Higher June 2019 Paper 4 Q12
12
(a) Here are the first four terms of a sequence.\[-1 \qquad 4 \qquad 9 \qquad 14\]
Write an expression for the \(n\)th term of this sequence. [2]
(b) The \(n\)th term of another sequence is given by\[an^2 + bn\]
The third term is 9 and the sixth term is 126.
Find the value of \(a\) and the value of \(b\). [5]
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| \(5n - 6\) or \(-1 + 5(n - 1)\) oe | 2 | condone \(+ -6\) etc for 2 marks B1 for \(5n + c\) | |
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| [\(a\) =] 6 [\(b\) =] −15 | 5 | B1 for \(3^2a + 3b = 9\) or better B1 for \(6^2a + 6b = 126\) or better M1 for equating the coefficients of a variable, e.g. \(18a + 6b = 18\), allow one numerical error M1 for correctly eliminating one variable, e.g. \(18a = 108\), allow one numerical error allow any correct method | |