The sum of the first n terms of an arithmetic progression is given by S_n = 2n^2 + 3n. Wha… — JAMB UTME

The sum of the first $n$ terms of an arithmetic progression is given by $S_n = 2n^2 + 3n$ . What is the value of the $7^{\text{th}}$ term of the progression?

Answer: 29

Answer

The

7^{\text{th}}

term of the arithmetic progression is

29

For any sequence, the

n

-th term is found using

T_n = S_n - S_{n-1}

. Substituting

n = 7

gives

S_7 = 2(7)^2 + 3(7) = 119

and

S_6 = 2(6)^2 + 3(6) = 90

. Thus,

T_7 = 119 - 90 = 29

Step-by-Step Solution

State the relationship between the

n

-th term

T_n

and the sum of first

n

terms

S_n

T_n = S_n - S_{n-1}

The sum of the first

n

terms minus the sum of the first

n-1

terms equals the

n

-th term.

Calculate the sum of the first 7 terms (

S_7

)

S_7 = 2(7)^2 + 3(7) = 119

Substitute

n = 7

into the sum formula

S_n = 2n^2 + 3n

Calculate the sum of the first 6 terms (

S_6

)

S_6 = 2(6)^2 + 3(6) = 90

Substitute

n = 6

into the sum formula

S_n = 2n^2 + 3n

Compute the

7^{\text{th}}

term (

T_7

)

T_7 = 119 - 90 = 29

Subtract

S_6

from

S_7

Key Concept

Relationship between the nth term and the sum of first n terms of an AP

Question

Answer

Step-by-Step Solution

Key Concept

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