Find the sum of each of the following APs: 9, 7, 5, 3, ... to 14 terms.

Question

Philoid · Accepted Answer

Here, first term = 9

Common difference = 7 - 9 = - 2

Sum of first n terms of an AP is

S_n = [2a + (n - 1)d]

∴ S₁₄ = [2(9) + (14 - 1)(-2)]

= (7)(18 - 26)

= (7) × (-8)

= - 56

Thus, sum of 14 terms of this AP is - 56.