d - a = 7
c - b = 2
b = a • q
c = a • q^2
d = a • q^3
aq^3 - a = 7
a • q^2 = a • q = 2 =>
a (q^3 - 1) = 7
a • q^2 - a • q = 2 =>
a (q - 1) (q^2 + q + 1) = 7
a • q (q - 1) = 2 =>
a (q - 1) (q^2 + q + 1) = 7 / a ( q - 1) = 2/q =>
2q^2 - 5q + 2 = 0 => D = 25 - 16 = 9
Q112 = 5 +_ 3 / 4 =>
Q1 = 2
Q2 = 1/2
Succes.
