Question

Calcule a soma dos dez primeiros termos da PG (-1, 3, -9, 27,...)

Answer 1

S_n = a_1(q^n-1)/q-1

q = 3/-1 = -3

S_10 = -1(-3^10-1) / -3-1

S_10 = -1(59049-1) / -4

S_10 = 59048 / 4

S_10 = 14762