diketahui deret aritmatika dengan U3=8 danU8=23.jumlah 25 suku pertama adalah

Bab Pola Bilangan

U3 = a + (3 - 1)b
a + 2b = 8

U8 = a + (8 - 1)b
a + 7b = 23

a + 7b = 23
a + 2b = 8
_________ _
5b = 15
b = 3

a + 2b = 8
a + 2(3) = 8
a = 8 - 6
a = 2

Sn = n/2 (2a + (n - 1)b)
S25 = 25/2 (2(2) + (25 - 1)3)
S25 = 25/2 (4 + 72)
S25 = 25/2 (76)
S25 = 25(38)
S25 = 950

langsung aja y

U3 = a + 2b = 8
U8 = a + 7b = 23
_____________-
-5b = -15
b = 3

a + 2b = 8
a = 8 - 2(3)
a = 8 - 6
a = 2

S25 = 25/2 (2a + 24b)
S25 = 12,5 (2.2 + 24.3)
S25 = 12,5 (4 + 72)
S25 = 12,5 (76)
S25 = 950

semonga berguna +_+