soal barisan dan deret.

DEret Aritmetika  a, (2b -1), (2a+2)
sifat
2(2b -1) = a + 2a + 2
4b - 2 = 3a + 2
4b = 3x + 4
8b = 2(3x + 4) = (6x + 8)
.
Deret Geo
1/(1+a) + 1/(1+a)² + 1/(1+a)³ + .... = 4a//
misal x = 1+a  dan a = x - 1
u1 = 1/x
u2 = 1/x²
r = 1/x
s~ = 4a = 4(x-1)
.
s~ = a/(1- r)
4(x-1) = (1/x) / (1 - 1/x)
4(x-1) = (1)/(x-1)
(x-1)² = 1/4
(x-1) = 1/2  atau x -1 = - 1/2
x = 3/2  attau x = 1/2
x = 3/2 -->.a = 1/x = 1/(3/2) = 2/3
x = 1/2 --> a = 1/x = 1/ (1/2) =  2

8b = 6x +8
x = 2/3  --> 8b = 6(2/3 ) + 8 = 12
x = 2 --> 8b = 6(2) + 8 = 20
..
nilai 8b = 12