.b1=3 q=-2 S4=?

Question

.b1=3
q=-2
S4=?

Answer 1

 b3=3
q=-2
S4-?
b4=b3*q^3=3*(-2)^3=3*(-8)=-24
S4=b1(q^4-1)/(q-1)=3((-2)^4-1)/-2-1=3*15/-3=3*15/-3=-15