u6 + u8 + u10 + u12 = 132
u2 + u4 = 18
Calculer sa raison r et son terme u1.
J'ai fais ca :
2+u4 = 2r+4r+u1 = 6r + u1
u6+u8+u10+u12 = 6r+8r+10r+12r+u1 = 36r + u1
18 - 132 = -114
6r - 36r = -30r
donc -114 = -30r
-114/30 = r
-3.8 = r
18 = u1 + 6r --------> u1 + 6*(-3.8) =18
-22.8 + 18 = -4.8
donc u1 = 4.8 et r = 3.8