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Sequence and Series

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Question : 12 of 86

Marks: +1, -0

Determine the first term of an A.P. with common difference

3

7^{\text{th}}

term being 11

$-7$
$7$
$6$
$5$

Solution:

Concept:

Use the formula for the

n^{\text{th}}

term of an arithmetic progression:

a_n = a + (n-1)d

.

Explanation:

Given: common difference

d = 3

,

7^{\text{th}}

term

a_7 = 11

.

Substitute into formula:

a + (7-1)\times 3 = 11

.

So

a + 18 = 11

.

Thus

a = 11 - 18 = -7

.

Answer:

The first term is

-7

.

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