Ответ:

q=-2, S5=5.5S5=b1*(q^5-1)/(q-1)=5.5b1*(-32-1)/(-2-1)=5.5b1*(-33)/-3=5.5b1*11=5.5b1=5.5/11=1/2=0.5b5=b1*q^4=0.5*16=8