Помогитеее плезb1 = -2,8q = 2S5 = ?

Question

Помогитеее плез
b1 = -2,8
q = 2
S5 = ?

Answer 1

S5=(b1*(1-q^5))/(1-q)=(-2,8*(1-2^5))/(1-2)=-2.8*-31/-1= -86.8

Answer 2

Sn=b1*(q^n-1)/(q-1)
S5=b1(q^5-1)/(q-1)=-2,8*(32-1)/(2-1)=-2,8*31=-86,8