Question

plz zzz tell correct answer. ​

Answer 1

Answer :-

$\large{\star\:\:\boxed{\bf{S_{25}\:=\:1025}}\:\:\star}$

Question :–

Find the Sum of first 25 terms of an arithmetic sequence 5, 8 , 11 , 14 ,...

Explanation :-

Given :–

5 , 8 , 11 , 14 ,...

where a = 5 and d = 3 .

To Find :–

S₂₅ (Sum of first 25 terms)

Formula Applied :–

$\boxed{\star\:\:\bf{S_{n}\:=\:\dfrac{n}{2}\:[2a\:+\:(n\:-\:1)d] }\:\:\star}$

Solution :–

We have ,

a = 5

d = 3

n = 25

Putting these values in the Formula :—

$\rightarrow\sf{S_{n}\:=\:\dfrac{n}{2}\:[2a\:+\:(n\:-\:1)d] }$

$\rightarrow\sf{S_{25}\:=\:\dfrac{25}{2}\:[2(5)\:+\:(25\:-\:1)(3)] }$

$\rightarrow\sf{S_{25}\:=\:\dfrac{25}{2}\:[10\:+\:(24\:\times\:3)] }$

$\rightarrow\sf{S_{25}\:=\:\dfrac{25}{2}\:(10\:+\:72) }$

$\rightarrow\sf{S_{25}\:=\:\dfrac{25}{2}\:\times\:82 }$

$\rightarrow\sf{S_{25}\:=\:25\:\times\:41 }$

$\rightarrow\boxed{\bf{S_{25}\:=\:1025}}$

∴ The Sum of first 25 terms is 1025 .

Answer 2

Answer:

A= 5

D= 3

$an = a \: + (n - 1)d$

$an \: = 5(25 - 1)3$

$an = 5(24) \times 3$

$an = 136 \times 3$

$an = 408$

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