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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  f ( x ) = e 2 sin ( π x 2 ) , for x > 0.

The k th maximum point on the graph of f has x-coordinate xk where  k Z + .

Given that xk + 1 = xk + a, find a.

[4]
a.

Hence find the value of n such that  k = 1 n x k = 861 .

[4]
b.

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]

a.

recognizing the sequence x1,  x2,  x3, …, xn is arithmetic  (M1)

eg  d = 4

correct expression for sum       (A1)

eg   n 2 ( 2 ( 1 ) + 4 ( n 1 ) )

valid attempt to solve for n      (M1)

eg  graph, 2n2n − 861 = 0

n = 21       A1 N2

[4 marks]

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Topic 1—Number and algebra » SL 1.2—Arithmetic sequences and series
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Topic 1—Number and algebra

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