1. Jika suku ke-n, 5(n) =1/6n (n+2) (2n+1) maka s8 adalah.... 2. Diketahui barisan bilangan. 2,4,8,14,22.....suku ke 10 ...... 3. Suki barisan aritmatika

Mapel : Matematika
Kelas : IX SMP
Bab : Barisan dan deret

Pembahasan :
1.

Sn = 1/6n(n + 2)(2n + 1)
S8 = 1/6(8)(10)(17)
S8 = 226,6

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2.

2A = [(8 - 4) - (4 - 2)]
2A = [4 - 2]
2A = 2
A = 1

3A + B = Beda
3(1) + B = 2
B = -1

A + B + C = 2
1 - 1 + C = 2
C = 2

Un = An² + Bn + C
U10 = (10)² - (10) + 2
U10 = 100 - 10 + 2
U10 = 92

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3.

Beda = (U7 - U3)/(7 - 3)
Beda = (15 - 7)/4
Beda = 8/4
Beda = 2

U3 = 7
a + 2b = 7
a + 2(2) = 7
a = 3

U30 = a + 29b
U30 = 3 + 29(2)
U30 = 3 + 58
U30 = 61

Sn = n/2(a + Un)
S30 = 30/2(3 + 61)
S30 = 15(64)
S10 = 960