Question

sum of first n terms of an arithametic sequence is 8n^2+5n.
a)find the sum of first 20 terms?
b)write the algebraic expression of the sequence?

friends can you please answer this question by step by step.​

Answer 1

Answer:

a)3300

b)16n-3

Step-by-step explanation:

First...

S(n)=8n^2+5n

thus, S(20)=3300

Second...

(b)S(n)=8n^2+5n

thus,

S(1)=13=first term of the sequence

S(2)=42 , the second term is (42-13)=16

because S(2) signifies sum of first 2 terms of the given sequence;

thus the common difference is (29-13)=16

thus we got a=13, d=16

hence the nth term as per (b) is 13+(n-1)*16

which is further simplified into 16n-3