hitunglah jumlah deret berikut : 3+5+7+.....51

Diket:
a = 3
b = 2

Tanya: Jumlahnya?

Jawab
51 = 3 + (n-1)(2)
51 = 3 + 2n - 2
51 - 3 + 2 = 2n
50 = 2n
n = 25

S25 = n/2 (2a + (n-1)b)
S25 = 25/2 (6 + (24)2)
S25 = 12,5 (6 + 48)
S25 = 12,5 × 54
S25 = 675

semoga membantu ^__^

a = 3
b = 5-3 = 2
un = a + (n-1) b
51 = 3 + (n-1) 2
51 = 3+ 2n - 2
51 = 1 - 2n
2n = 1 - 51
2n = -50
n = -50/2
n = -25
n tidak mungkin negatif jadi n = 25
sn = 25/2 (2a + (n-1) b )
S25= 25/2 (2.3 + 24.2)
= 25/2 (6 + 48)
= 25/2 (54)
= 25 (27)
= 675