jika 3+5+7+...+k=440. maka nilai k adalah?

Kelas 8 Matematika
Bab Barisan dan Deret Bilangan

3 + 5 + 7 + ... + k = 440

b = U2 - U1
b = 5 - 3
b = 2

Sn = 440
n/2 . (2a + (n - 1) . b) = 440
n/2 . (2 . 3 + (n - 1) . 2) = 440
n/2 . (6 + (n - 1) . 2) = 440
n (3 + n - 1) = 440
n² + 2n - 440 = 0
(n + 22) (n - 20) = 0
n + 22 = 0
n = -22 (tidak memenuhi karena negatif)

n - 20 = 0
n = 20

Un = a + (n - 1) . b
U20 = 3 + 19 . 2
U20 = 3 + 38
U20 = 41

k = 41