Analysis and Approaches for IBDP Maths Ebook 1 | Page 63

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20
Paper 2 Section A – Finding
and
with given three terms
Example
The first three terms of an arithmetic sequence are u1 � 0.6 , u2 � 2.7 , u3 � 4.8 .
(a)
(b)
(c)
Find the common difference.
Find the 43th term of the sequence.
Find the value of
43
� un
.
n�1
[2]
[2]
[2]
5
Solution
(a) d �2.7 � 0.6
(M1) for valid approach
d � 2.1
A1 N2
[2]
(b) u43 � 0.6 � (43� 1)(2.1)
(A1) for correct substitution
(c)
u43 � 88.8
A1 N2
43
�
u
n
n�1
� S 43
� 43 � 2(0.6) � (43 � 1)(2.1) �
(A1) for correct substitution
2
� 1922.1
A1 N2
[2]
[2]
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