Question

Tentukan jumlah bilangan deret 1+3+5+7+....+19

Answer 1

Verified answer

1+3+5+7+...+19

a = 1
b = 3 - 1 = 2
Un = a + (n - 1)b
19 = 1 + (n - 1) × 2
19 = 1 + 2n - 2
19 = 2n - 1
2n = 19 + 1
2n = 20
n = 20/2
n = 10

Dn = 1/2(n)[2a + (n - 1)b]
D10 = 1/2(10)[2(1) + (10 - 1) × 2]
D10 = 5[2 + 9 × 2]
D10 = 5[2 + 18]
D10 = 5 × 20
D10 = 100

Jadi jumlah bilangan deret tersebut adalah 100