tolong kerjakan no 5&7 pakai cara tolong

5. U4 = 4
    a+(4-1)b = 4
    a+3b = 4
    U9 = 34
    a+8b = 34
    a+3b = 4
(dikurangi)
5b=30
b= 6
a+3b = 4
a+3.6 =4
a+18 = 4
a = -14
U15= a+14b = -14+ 14.6 = 70
U5 = a+4b = -14 + 4.6= -14 + 24 = 10
U15/U5 = 70/10 = 7

7. Sn = n/2 (2a+(n-1)b)
  
     S8 = 144
     144 = 8/2 (2a+7b)
     144 = 4 (2a+7b)
     36 = 2a+7b . . . . . . (1)
     U6 = 6
     a+5b = 6 ..........(2)
  
     2a+7b = 36.. . . . . . . . 2a+7b = 36
     a+5b = 6 (x 2) . . . . . . 2a+10b = 12
                                         (dikurangi)
-3b=24
b= -8

a+5b = 6
a+5(-8) = 6
a-40 = 6
a=46

U9= a+8b= 46+8.(-8) = 46-64 = -18
U11= a+10b = 46+10.(-8) = 46-80 = -34
U9+U11 = -18-34 = -52