Question

Find the sum of the following APs:

–37, –33, –29, ... to 12 terms.

Answer 1

–37, –33, –29, ... to 12 terms

For this A.P.,

a = –37

d = a₂ – a₁ 

= (–33) – (–37)

= –33 + 37

= 4

n = 12

We know that,

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

S₁₂ = `12/2 [2(-37) + (12 - 1) × 4]`

= 6[–74 + 11 × 4]

= 6[–74 + 44]

= 6(–30)

= –180

Thus, the sum of first 12 terms is –180.