Question

Find the sum of the following APs:

9, 7, 5, 3, ... to 14 terms.

Answer 1

The given AP is 9, 7, 5, 3,...

Here, a = 9 and d = 7 – 9 = –2

Using the formula, `S_n = n/2 [2a + (n - 1)d]`, we have

`S_14 = 14/2 [2 xx 9 + (14 - 1) xx (-2)]`

= 7 × (18 – 26)

= 7 × (–8)

= –56