Question

an=2n then find the value of s3​

Answer 1

The value of $S_{3}$ is "12".

Step-by-step explanation:

We have,

$a_{n}$ = 2n  

Put n = 1, 2, 3, ..... , n

∴ $a_{1}$ = 2 × 1 = 2,  $a_{2}$ = 2 × 2 = 4,

$a_{3}$ = 2 × 3 = 6, ....

The series becomes,

2, 4, 6, ......, n

The  above sequence is an arithmetic progression.

Here, first term(a) = 2, common difference(d) = 4 - 2 = 2 and number of terms(n) = 3

To be find $S_{3}$  = ?

We know that,

$S_{n}$  = $\frac{n}{2}$·{2a + (n - 1)d}

∴ $S_{3}$  = $\frac{3}{2}$·{2 × 2 + (3 - 1)·2}

⇒$S_{3}$  = $\frac{3}{2}$·{4 + 4}

⇒$S_{3}$ = $\frac{3}{2}$·{8}

⇒$S_{3}$ = 12

Hence, the value of $S_{3}$ is 12.

Answer 2

Answer:

Step-by-step explanation:

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