Dik: u3=8, u5=32 Dit: s8?

Mapel : Matematika

Kelas : 9

Bab : Barisan dan Deret Bilangan
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U3 = 8
U5 = 32

Ditanya → S8

Jawaban :
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→ Tentukan beda barisan

U5 - U3 = 32 - 8
5b - 3b = 24
2b = 24
b = 24/2
b = 12

→ Tentukan nilai a barisan

U3 = 8

a + (3-1)b = 8
a + 2(12) = 8
a + 24 = 8
a = 8 - 24
a = -16


Maka, jumlah 8 suku pertama barisan :

Sn = n/2 [2a + (n - 1)b]

S8 = 8/2 [2*(-16) + (8-1)(12)]

S8 = 4 [-32 + 84]

S8 = 4 x 52

S8 = 208 ✔

Diketahui U3 = a+2b = 8
U5 = a+4b = 32

• Eliminasi
a+2b = 8
a+4b = 32
--------------- _
-2b = -24
b = 12
Maka a = -16

•Sn = n/2 ×(2a+(n-1)b)
S8 = 4 × (-32 + 84)
= 4 × 52
= 208

Dicek lagi yaa, maaf kalau salah:(