Date | May 2018 | Marks available | 4 | Reference code | 18M.2.SL.TZ1.S_7 |
Level | Standard Level | Paper | Paper 2 | Time zone | Time zone 1 |
Command term | Find | Question number | S_7 | Adapted from | N/A |
Question
Let , for x > 0.
The k th maximum point on the graph of f has x-coordinate xk where .
Given that xk + 1 = xk + a, find a.
Hence find the value of n such that .
Markscheme
* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.
valid approach to find maxima (M1)
eg one correct value of xk, sketch of f
any two correct consecutive values of xk (A1)(A1)
eg x1 = 1, x2 = 5
a = 4 A1 N3
[4 marks]
recognizing the sequence x1, x2, x3, …, xn is arithmetic (M1)
eg d = 4
correct expression for sum (A1)
eg
valid attempt to solve for n (M1)
eg graph, 2n2 − n − 861 = 0
n = 21 A1 N2
[4 marks]