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Date November 2019 Marks available 2 Reference code 19N.2.SL.TZ0.S_5
Level Standard Level Paper Paper 2 Time zone Time zone 0
Command term Find Question number S_5 Adapted from N/A

Question

The first two terms of a geometric sequence are u1=2.1 and u2=2.226.

Find the value of r.

[2]
a.

Find the value of u10.

[2]
b.

Find the least value of n such that Sn>5543.

[3]
c.

Markscheme

valid approach        (M1)

eg       u1u2,  2.2262.1,  2.226=2.1r

r=1.06  (exact)       A1  N2

[2 marks]

a.

correct substitution        (A1)

eg       2.1×1.069

3.54790       A1  N2

u10=3.55

[2 marks]

b.

correct substitution into Sn formula        (A1)

eg      2.1(1.06n1)1.061,  2.1(1.06n1)1.061>5543,  2.1(1.06n1)=332.58,  sketch of Sn and y=5543

correct inequality for n or crossover values       A1

eg       n>87.0316,  S87=5532.73  and  S88=5866.79

n=88       A1  N2

[3 marks]

c.

Examiners report

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

Syllabus sections

Topic 1—Number and algebra » SL 1.3—Geometric sequences and series
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Topic 1—Number and algebra

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