Tentukan jumlah setiap deret berikut :
a. 12+15+18+….+126
b. 2+1+½+…+1/32
Jawaban Terkonfirmasi
Jawab
a.)
a= 12
b = 3
un = 3n + 9
un = 3n +9 = 126
3n = 117
n = 39
S39= 39/2 (12 + 126)=2.691
b)
a= 2
r= 1/2
un = arⁿ⁻¹ = 1/32
2¹. (2⁻¹)ⁿ⁻¹ = 2⁻⁵
1 -1(n-1) = -5
1 – n+ 1= -5
-n + 2 = -5
-n = – 7
n =7
S7 = a( 1- r⁷) / ( 1- r)
S7 = 2 (2)(1 – 1/2⁷)
S7= 4(1 – 1/2 ⁷)
S7 = 4 (127/128)
S7= 127/32