tolong jawab soal no 39 & 40 .beserta cara kerjanya.... tolong bantuannya yaahh

39.Ut = -3/8
U2t-1 = -6
r = -2

Ut = √U1.U2t-1
Ut² = U1.U2t-1
(-3/8)² = U1.-6
9/64×-1/6 = U1
U1 = -3/128.

Un = U1r^n-1
-6 = -3/128 × -2^n-1
-6 × -128/3 = -2^n-1
256 = -2^n-1
-2^8 = -2^n-1
8= n-1
n = 9. (D)

40.r = 3
S5 = 20 1/6

Sn = U1(r^n -1)
           r-1
20 1/6 = U1(3^5 -1)
                   3-1
121/6 = 242.U1
              2
242 = 1452.U1
U1 = 242
     1452
U1 = 1/6. (A)