jumlah 12 suku pertama deret 3+7+11+15... sama dengan ...

3 + 7 + 11 + 15 + ...
a = 3
b = 7 - 3 = 4

U12 = a + 11b
= 3 + 11(4)
= 3 + 44
= 47

Sn = n/2 (a + Un)
S12 = 12/2 (3 + 47)
S12 = 6(50)
S12 = 300

Bab Barisan dan Deret
Matematika SMP Kelas IX

a = 3
b = 7 - 3 = 4

Sn = n/2 x (2a + (n - 1) b )
S12 = 12/2 x (2 x 3 + 11 x 4)
S12 = 6 x (6 + 44)
S12 = 6 x 50
S12 = 300