It is given that,
a4 + a8 = 24
⇒ a + 3d + a + 7d = 24
⇒ 2 a+ 10d = 24
⇒ a + 5d = 24 (i)
And,
a6 + a10 = 44
⇒ a + 5d + a + 9d = 44
⇒ 2a + 14d = 44
⇒ a + 7d = 22 (ii)
solving (i) and (ii) we get
a = –13 and d = 5
Hence, the first three terms are
a, a + d, a + 2d
⇒ – 13, (–13 + 5), (–13 + 2 x5)
= –13, –8,–3
⇒ 2a + 14d = 44
Problems Based on sum of ‘n’ th term of an A .P
The first and the last term of an A .P. are 4 and 81 respectively. If the common difference is 7, how many terms are there in the A .P. and what is their sum?