Apps. and Interpretation for IBDP Maths Ebook 1 | Page 71

4. In an arithmetic sequence, the general term is given by u
n
, and the sum of the first n
terms is given by
S
n
2
n �19n
� .
28
(a) (i) Write down the values of S
1
and S
2
.
(ii) Hence, write down the values of u
1
and u
2
.
(b)
(c)
(d)
(iii)
Find the common difference of the sequence.
Find the smallest value of n such that
Find the value of
100
� ur
.
r�50
Find u
n
in terms of n .
n
� ur
�100
.
r�1
58
(e) Find the value of n such that un
�2un
� 1
� .
7
[6]
[3]
[3]
[2]
[3]
7
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