Question

Найдите сумму первых 5-и членов геометрической прогрессии, если b4=9, q=1/3.

Answer 1

^^ - степень

b4=9, q=1/3.

b4 = b1* q^n-1^

9 = b1 * 1/3^3^

1/27b1 = 9

b1 = 1/3     

S5 = {b1*(q^n-1^)} / q-1

S5 = 1/3* 1/3^4^ = 1/3 * 1/81 = 1/243

 1/243  /   -2/3 =  -1/162