jumlah deret:4+9+14+....+104 adalah

1134
Semoga bermanfaat

a = 4
b = 9 - 4 = 5
un = a + n-1 × b
104 = 4 + (n-1) × 5
104 = 4 + 5n - 5
5n = 104 - 4 + 5
5n = 105
n = 21.
sn = n/2 ( a + un )
sn = 21/2 ( 4 + 104 )
sn = 21/2 × 108
sn = 21 × 54
sn = 1134