Date | May 2018 | Marks available | 3 | Reference code | 18M.1.AHL.TZ2.H_5 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 2 |
Command term | Find | Question number | H_5 | Adapted from | N/A |
Question
The geometric sequence u1, u2, u3, … has common ratio r.
Consider the sequence .
Show that A is an arithmetic sequence, stating its common difference d in terms of r.
A particular geometric sequence has u1 = 3 and a sum to infinity of 4.
Find the value of d.
Markscheme
* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.
METHOD 1
state that (or equivalent) A1
attempt to consider and use of at least one log rule M1
A1
(which is an AP) with (and 1st term ) A1
so A is an arithmetic sequence AG
Note: Condone absence of modulus signs.
Note: The final A mark may be awarded independently.
Note: Consideration of the first two or three terms only will score M0.
[4 marks]
METHOD 2
consideration of M1
M1
A1
which is constant R1
Note: Condone absence of modulus signs.
Note: The final A mark may be awarded independently.
Note: Consideration of the first two or three terms only will score M0.
attempting to solve M1
A1
A1
[3 marks]