Question

The sum of first n terms of an AP is (5n^2/2+3n/2). Find the nth term and the 20th term of this AP.

Answer 1

Answer:

nth term = 5n - 1

20th term = 99

Step-by-step explanation:

Sum

=n/2(5n +3)

=n/2(3+5(n-1)+5)

=n/2(8+5(n-1))

comparing with Sn = n/2(2a+d(n-1)),

a = 4

d = 5

nth term = a + (n-1)d = 4 + 5(n-1) = 5n - 1

20th term = 5×20-1 = 99