Find the sums given below:
34 + 32 + 30 + . . . + 10
Let ‘a’ be the firs term and ‘d’ the common difference, then
a = 34, d = –2, an = 10 = l
We know that,an = a + (n – 1)
⇒ 10 = 34 + (n – 1) (–2)
⇒ 10 = 34 –2n + 2
⇒ 10 = 36 – 2n
⇒ –26 = –2n ⇒ n = 13