Apps. and Interpretation for IBDP Maths Ebook 1 | Page 64

Your Practice Set – Applications and Interpretation for IBDP Mathematics
17
Paper 1 – Finding and with Given 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
30
30 2
1 (30 1)
2
30
S30
� � 2(3) � (30 � 1)(4) �
(A1) for correct substitution
2
S30 � 1830
A1 N2
(c) S � � u � � d�
[2]
[2]
[2]
54
SE Production Limited