Analysis and Approaches for IBDP Maths Ebook 1 | Page 58

Your Practice Set – Analysis and Approaches for IBDP Mathematics
17
Paper 1 Section A – Finding
and
with given two terms
Example
In an arithmetic sequence, u1 � 3 and u4 � 15 .
(a) Find d .
(b) Find u
30
.
(c) Find S
30
.
[2]
[2]
[2]
Solution
(a)
u4 � u1
d �
3
(M1) for finding d
15 � 3
d �
3
d � 4
A1 N2
(b) u30 � u1 � (30 � 1) d
u30 � 3 � (30 � 1)(4)
(A1) for correct substitution
u30 � 119
A1 N2
[2]
30
S30 � 2 u1
� (30 � 1) d
2
30
S30
� � 2(3) � (30 � 1)(4) �
(A1) for correct substitution
2
S30 � 1830
A1 N2
[2]
(c) � �
[2]
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