Question

геометрик прогрессия. b1-b14=30 q=-1/2 s13=?

Answer 1

b1-b1q^13=30
b1(1-q^13)=30
b1=30/(1-q^13)
S13=b1*(1-q^13)/(1-q)
S13=30/(1-q^13)*(1-q)13)/(1+0,5)=30/1,5==20