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WAEC Further Mathematics 2015 Paper

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Question : 37

Total: 40

The sum,

S_{n}

, of a sequence is given by

S_{n} = 2n^{2} - 5

. Find the 6th term.

112
67
45
22

Solution:

Concept:

For a sequence whose sum of first

n

terms is

S_n

, the

n

th term is given by

T_n = S_n - S_{n-1}

.

Explanation:

Given

S_n = 2n^2 - 5

.

To find the 6th term, use

T_6 = S_6 - S_5

.

First,

S_6 = 2(6^2) - 5 = 2(36) - 5 = 72 - 5 = 67

.

Next,

S_5 = 2(5^2) - 5 = 2(25) - 5 = 50 - 5 = 45

.

Therefore,

T_6 = 67 - 45 = 22

.

Answer:

The 6th term is

22

, which is option D.

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