Question

Найдите сумму геометрической прогрессии bn

Answer 1

$\displaystyle S = \frac{b_1}{1-q} = \frac{-8}{1+1/2} = -5\frac{1}{3}$

Answer 2

bn=(-1)ⁿ*16/2ⁿ   bn/bn-1=q

      (-1)ⁿ*16*2ⁿ⁻¹
q= ----------------- = - 1/2      s=b1*(1-q)ⁿ/(1-q)   b1=-16/2=-8
       2ⁿ (-1)ⁿ⁻¹*16

sn=-8*(3/2)ⁿ*2/3=-16/3*(3/2)ⁿ