In an A.P.
Given l = 28, S = 144, n = 9, find ‘a’.
Here, l = 28, S = 144
n = 9
l = a + (n – 1)d
28 = a + (9 – 1)d
⇒ 28 = a + 8d ...(i)
And,
32 = 2(a + 4d)
a + 4d = 16 .....(ii)
Solving (i) and (ii) we get,
a = = 32 -28 = 4
Hence , a = 4
The first term of an AP is 5, the last term is 45 and the sum is 400. Find the number of terms and the common difference.