Question

Find the sum of the following AP:

-37, -33, -29,…, to 12 terms.

Answer 1

Given A.P: -37, -33, -29,…, to 12 terms. 

a = -37; d = a₂ – a₁ = (-33) – (-37) = -33 + 37 = 4; n = 12 

S_n = \(\frac{n}{2}\) [2a + (n – 1)d] 

∴ S₁₂ = \(\frac{12}{2}\) [2 × (-37) + (12 – 1)4] 

= 6 [-74 + 11 × 4] 

= 6 [-74 + 44] 

= 6 × (-30) 

= -180