b1*q^2-b1=9
b1*q-b4*q^3=18
b1*(q^2-1)=9
b1*(q-q^3)=18
3b1=3
b1=3
9/(q^2-1)=18/(q-q^2)
q=-2
b2=-6 b3=12 b4=-24
b1*q^2-b1=9
b1*q-b4*q^3=18
b1*(q^2-1)=9
b1*(q-q^3)=18
3b1=3
b1=3
9/(q^2-1)=18/(q-q^2)
q=-2
b2=-6 b3=12 b4=-24