Jumlah 5 suku pertama barisan 9,6,3 Adalah.?

Mapel : Matematika

Kelas : 9

Bab : Barisan dan Deret Bilangan
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9, 6, 3

a = 9
b = 6 - 9 = -3
n = 5


Jumlah 5 Suku Pertama Barisan

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

S5 = 5/2 [2(9) + (5-1)(-3)]

S5 = 5/2 [18 - 12]

S5 = 5/2 x 6

S5 = 30/2

S5 = 15

b = U2-U1
   = 6-9
   = -3

U1= 9
 
Sn= n/2 (2a+(n-1)b)
     = 5/2 (2(9)+(5-1)-3)
     = 5/2 (18+(-12)
     = 5/2 (6)
     = 5/2 * 6
     = 15