Jawabanmu

2014-02-26T11:20:34+07:00
U2=ar=81. U5=ar^4=3. r^3=1/27. r=1/3. ar=81. 1/3a=81. a=243. U8=ar^7=81*1/2187=1/9
2014-02-26T12:58:07+07:00
U2= a+b =81
U5= a+4b= 3
sistem eliminasi hasilnya -3b=78
b=-26
masukin ke persamaan 1 atau 2. a+b= 81
a+ (-26) = 81
a= 107
U8 = 107+ 7.(-26) = -75
eh maaf itu aritmatika
diket u2=a.r=81
u5=ar^4= 3
u5:u2
ar=81:ar^4=3
r^3=1/27, r= 1/3
u2= a.1/3=81; a=81.3=243
u8= ar^7= 243.1/3^7= 0,1111