jika 1+3+5+7+9.....k=625,maka k=.....

Kelas 8 Matematika
Bab Barisan dan Deret

b = U2 - U1
b = 3 - 1
b = 2

Sn = 625
n/2 . (2a + (n - 1) . b) = 625
n/2 . (2 . 1 + (n - 1) . 2) = 625
n/2 . (2 + 2n - 2) = 625
n/2 . 2n - 625 = 0
n² - 625 = 0
(n + 25) (n - 25) = 0
n + 25 = 0
n = -25 (tidak memenuhi karena negatif)

n - 25 = 0
n = 25

Un = a + (n - 1) b
k = 1 + (25 - 1) . 2
k = 1 + 24 . 2
k = 1 + 48
k = 49