Deret goemetri : Dik : U5 = 8 U10 = -256 Dit : a / suku pertama ? r / rasio ? S10 ?

U5 = a + 4b = 8 ....... (1) U10 = a + 9b = -256 ..... (2) e. Pers 1 dan 2 a + 4b = 8 a + 9b = -256_ -5b = -248 b = 49.3 subs. b = 49.3 a + 4b = 8 a + 4(49.3) = 8 a + 197.2 = 8 a = -189.2 S10 = 1/2n{2a + (n-1)b } = 5(378.4 + 9*49.3) = 5(378.4 + 443.7) = 5*822.1 = 4110.5

u5=ar^4=8
u10=ar^9=-256
r=(u10/u5)=(ar^9)/(ar^4)=r^5=(-256/8)=-32
r^5=-32
r=-2

ar^4=8
a(-2)^4=8
a(16)=8
a=(8/16)=1/2