b1 = 1/9
b5 = b1*q^4 = 9
b5/b1 = 9 : 1/9 = 81
q^4 = 81
q = +- 3
1. q = 3
b2 = b1*q = 1/9*3 = 1/3
b3 = b2*q = 1/3*3 = 1
b4 = b3*q = 1*3 = 3
2. q = -3
b2 = b1*q = 1/9*(-3) = -1/3
b3 = b2*q = (-1/3)*(-3) = 1
b4 = b3*q = 1*(-3) = -3
b1 = 1/9
b5 = b1*q^4 = 9
b5/b1 = 9 : 1/9 = 81
q^4 = 81
q = +- 3
1. q = 3
b2 = b1*q = 1/9*3 = 1/3
b3 = b2*q = 1/3*3 = 1
b4 = b3*q = 1*3 = 3
2. q = -3
b2 = b1*q = 1/9*(-3) = -1/3
b3 = b2*q = (-1/3)*(-3) = 1
b4 = b3*q = 1*(-3) = -3