Find the sum of first 28 terms of an A.P. whose nth term is 4n -3.

Solution :

tn = 4n - 3

n = sum of 28 terms = 28

Sn = (n/2) [2a + (n - 1)d]

= (28/2) [2(1) + (28 - 1)4]

= 14[2 + 27(4)]

= 14 [110]

= 1540

Hence the sum of 28 terms of the given sequence is 1540.