Question

If the sum of n terms of an AP is given by 5n^2 - 2n, then find its 17th term is?​

Answer 1

Since the sum of n terms of an AP is given by

$5 {n}^{2} - 2n$

On putting n=1

S1=5(1)^2-2(1)

S1=3

Now since the sum of 1 term is equal to the term

So S1=3=a

On putting n=2

S2=5(4)-2(2)

S2=20-4

S2=16

=>a+(a+d)=16

2a+d=16

6+d=16

=>d=10

Therefore,

a17=a+16d

=3+160

a17=163

Therefore the 17th term of the AP is 163.

Hope it is helpul