Question

If S_n.., the sum of first n terms of an AP is given by S_n =3n²- 4n, find the nth term.  

Answer 1

s_n-=3n² - 4n 
Let S_n-1 be sum of (n - 1) terms

t_n = S_n - S_n-1
 (3n² - 4n) - [3(n - 1)²- 4(n- 1)]
=(3n²- 4n) - [3n² - 6n + 3 - 4n+4]
= 3n² - 4n - 3n² + 10n- 7
: . t_n =6n - 7
Therefore, required nth term =60- 7