Back to: Further Mathematics SS1

**Sequence & Series**

A sequence is a pattern of numbers arranged in a particular order. Each of the number in the sequence is called a term. The terms are related to one another according to a well defined rule.

Consider the sequence 1, 4, 7, 10, 13 …., 1 is the first term,(T_{1}) 4 is the second term(T_{2}), 7 is the third term (T_{3}).

The sum of the terms in a sequence is regarded as series. The series of the above sequence is

1 + 4 + 7 + 10 + 13 = 35

**The nth term of a Sequence**

The nth term of a sequence whose rule is stated may be represented by T_{n}so that T_{1}, T_{2}, T_{3}etc represent the first term, second term, third term … etc respectively.

Consider the sequence 5, 9, 13, 17, 21 ……..

T_{1} = 5 + 4(0)

T_{2} = 5 + 4(1)

T_{3} = 5 + 4 (2)

T_{4 }= 5 + 4 (3)

T_{n} = 5 + 4 (n – 1)

T_{n} = 5 + 4n – 4 = 4n +1

when n = 30

T_{30} = 4(30) + 1

T_{30} = 121

Find the nth term of these sequences:

(i) 3, 5, 7, 9 …… 2n + 1

(ii) 0, 1, 4, 9 ……… (n -1)^{2 }

(iii) 1/3, 3/4, 1, 7/6 ………………__2n – 1__

^{ }n + 2

__Arithmetic Mean__

If a, b, c are three consecutive terms of an A.P, then the common difference, d, equals

b – a = c – b = common difference.

b + b = a +c

2b = a + c

b = ½(a +c)

**Examples**

(i) Insert four arithmetic means between -5 and 10.

(ii) The 8^{th} term of a linear sequence is 18 and the 12^{th} term is 26. Find the first term, the common difference and the 20^{th} term.

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