Question

Qual a soma dos termos da p.a ( -61, -54, -47,..., 296, 303) ?

Answer 1

An = a₁ + (n - 1) * r

303 = - 61 + (n - 1) * 7

303 = - 61 + 7n - 7

303 = 7n - 68

7n = 303 + 68

7n = 371

n = 371/7

n = 53

Sn = (a₁ + an) * n / 2

S₅₃ = ( -61 + 303) * 53 / 2

S₅₃ = 242 * 53 / 2

S₅₃ = 121 * 53

S₅₃ = 6 413