jumlah deret 6+9+12+75+...+66

Mapel : Matematika

Kelas : 8, 9

Bab : Barisan dan Deret bilangan
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6, 9, 12, 15,... + 66


→ a = 6

→ b = 9 - 6 = 3


→ Tentukan banyak suku barisan (n)

Un = 66

a + (n - 1)b = 66

6 + (n - 1)(3) = 66

6 + 3n - 3 = 66

3n = 66 - 3

3n = 63

n = 63/3

n = 21



Maka, jumlah 21 suku pertama adalah


Sn = n/2 (a + Un)

S21 = 21/2 (6 + 66)

S21 = 21/2 ( 72)

S21 = 21 x 36

S21 = 756 ✔