Date | May 2017 | Marks available | 4 | Reference code | 17M.1.AHL.TZ2.H_3 |
Level | Additional Higher Level | Paper | Paper 1 (without calculator) | Time zone | Time zone 2 |
Command term | Find | Question number | H_3 | Adapted from | N/A |
Question
The 1st, 4th and 8th terms of an arithmetic sequence, with common difference d, d≠0, are the first three terms of a geometric sequence, with common ratio r. Given that the 1st term of both sequences is 9 find
the value of d;
the value of r;
Markscheme
* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.
EITHER
the first three terms of the geometric sequence are 9, 9r and 9r2 (M1)
9+3d=9r(⇒3+d=3r) and 9+7d=9r2 (A1)
attempt to solve simultaneously (M1)
9+7d=9(3+d3)2
OR
the 1st, 4th and 8th terms of the arithmetic sequence are
9, 9+3d, 9+7d (M1)
9+7d9+3d=9+3d9 (A1)
attempt to solve (M1)
THEN
d=1 A1
[4 marks]
r=43 A1
Note: Accept answers where a candidate obtains d by finding r first. The first two marks in either method for part (a) are awarded for the same ideas and the third mark is awarded for attempting to solve an equation in r.
[1 mark]