Date | May 2022 | Marks available | 2 | Reference code | 22M.1.SL.TZ2.2 |
Level | Standard Level | Paper | Paper 1 (without calculator) | Time zone | Time zone 2 |
Command term | Find | Question number | 2 | Adapted from | N/A |
Question
The nnth term of an arithmetic sequence is given by un=15-3nun=15−3n.
State the value of the first term, u1u1.
Given that the nnth term of this sequence is -33−33, find the value of nn.
Find the common difference, dd.
Markscheme
u1=12u1=12 A1
[1 mark]
15-3n=-33 15−3n=−33 (A1)
n=16n=16 A1
[2 marks]
valid approach to find dd (M1)
u2-u1=9-12u2−u1=9−12 OR recognize gradient is −3−3 OR attempts to solve -33=12+15d−33=12+15d
d=-3d=−3 A1
[2 marks]
Examiners report
A large majority of candidates earned full marks for this question. In part (a), a surprising number of candidates did not substitute n=1n=1 into the given expression, erroneously stating u1=15u1=15. Many of these candidates were able to earn follow-through marks in later parts of the question. In part (b), algebraic errors led a few candidates to find inappropriate values for nn, such as n=-6n=−6.