Question

If sum of n terms of an A.P. is n^2+5n then find general term.​

Answer 1

Answer:

3 + 4n

Step-by-step explanation:

Sum of first n terms of AP, Sn = 2n2 + 5n

Now choose n =1 and put in the above formula,

First term = 2+5 = 7

Now put n=2 to get the sum of first two terms = 2x4 + 5x 2= 8 + 10 = 18

This means  

first term + second term = 18

but first term =7 as calculated above

so, second term = 18-7 = 11

So common difference becomes, 11-7 = 4

So the AP becomes, 7, 11, 15, ..

nth term = a + (n - 1)d = 7 + (n-1)4 = 7 + 4n - 4 = 3 + 4n

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