diketahui deret aritmatika 4+9+14+19+...+59. Jumlah dari deret tsb adalah...

a = U1 = 4

b = U2 - U1
b = 9 - 4
b = 5

Un = 59
a + (n - 1) . b = 59
4 + (n - 1) . 5 = 59
4 + 5n - 5 = 59
5n - 1 = 59
5n = 59 + 1
5n = 60
n = 60 : 5
n = 12

S12 = n/2 . (a + Un)
S12 = 12/2 . (4 + 59)
S12 = 6 . 63
S12 = 378