Question

If for an A.P tn =8n-5 find sn

Answer 1

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Answer :

$S_n=3n^2$

Step-by-step explanation :

Given , $n^{th}term=t_n=8n-5$

=> 1st term = a = 8(1) - 5

=> a = 3

2 nd term = 8(2) - 5

=> 9

So common difference , d = 9 - 3 = 6

=> d = 6

$S_n=\frac{n}{2}[2a+(n-1)d]\\\\ =>S_n=\frac{n}{2}[2(3)+(n-1)6]\\\\=>S_n=\frac{n}{2}[6+6n-6]\\\\ =>S_n=\frac{n}{2}[6n]\\\\ =>S_n=3n^2$

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