O-LevelMathematicsAlgebra and graphs4024/22 · May/June 2014 · Q68 Marks
The first five terms of a sequence are 17, 11, 5, -1, -7. Find, in terms of n, an expression for the nth term of this sequence.
- (a)The first five terms of a sequence are 17, 11, 5, -1, -7. Find, in terms of n, an expression for the nth term of this sequence.[2]
- (b)(i)The nth term, S_n, of a different sequence is found using the formula S_n = n² + 3n. Work out the first four terms of this sequence.[2]
- (b)(ii)The nth term, T_n, of another sequence is found using the formula T_n = 5n – 12. There are two values of n for which S_n / T_n = 6. Form and solve an equation in n to find these two values.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.
- [2] (a) 23-6n cao
- [2] (a) B1 for -6n soi
- [2] (b)(i) 4, 10, 18, 28
- [2] (b)(i) B1 for 3 correct terms seen
- [4] (b)(ii) 3 and 24
- [4] (b)(ii) M1 for (n² + 3n) / (5n - 12) = 6 or better M1 for n² - 27n + 72 = 0 B1 for either 3 or 24
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