If the sum of first n terms of an A.P. is 1/2(3n^2 + 7n), then find its n^th term. Hence write its 20^th term.

Question

If the sum of first n terms of an A.P. is \(\frac{1}{2}\)(3n² + 7n), then find its n^th term. Hence write its 20^th term.

Answer 1

d = 3 

a_n = a + (n – 1)d 

= 5 + (n – 1) 3 

= 5 + 3n – 3 

= 3n + 2 

a₂₀ = 3(20) + 2 

= 60 + 2 = 62

 Hence, it’s 20^th term is 62