Question

if the sum of first n term of an ap is 2n² + 5n then find the 4 term​

Answer 1

Hey MATE!!!

From the question the sum of n terms is given by :

2n^2 + 5n

If we put n as 1 we get the sum of 1st term, then this will give us the 1st term of AP.

n= 1 => 2*1*1+5*1=> 7 = a1

To find a2, we put n as 2 and get the sum of 1st two terms of AP <S2>.

To find a2, we put n as 2 and get the sum of 1st two terms of AP <S2>.Then we subtract 7 <a1> from the sum

To find a2, we put n as 2 and get the sum of 1st two terms of AP <S2>.Then we subtract 7 <a1> from the sum which will give us the 2nd term of AP.

n=2 ==> 2*2*2 + 5*2 => 18 =>S2

Now, S2 - a1 = a2.

18 - 7 = 11 => a2

Hence, the AP is 7,11,15,19...

Hence, a4 => 19 Answer

Hope it helps

HAKUNA MATATA :))