suku ketiga dari suatu barisan aritmatika = 9 sedangkan suku ke-8 = 4 Tentukan suku ke-15

U3 = 9
a + (n - 1) b = 9
a + (3 - 1) b = 9
a + 2 b = 9 ..........(1)

U8 = 4
a + (n - 1) b = 4
a + (8 - 1) b = 4
a + 7 b = 4 ..........(2)

(2) dan (1) dieliminasi

a + 7 b = 4
a + 2 b = 9
--------------- --
5 b = -5
b = -5/5
b = -1

b = -1 subtitusi ke (1)
a + 2b = 9
a + 2 . (-1) = 9
a - 2 = 9
a = 9 + 2
a = 11

Un = a + (n - 1) b
U15 = 11 + (15 - 1) (-1)
U15 = 11 + 14 . (-1)
U15 = 11 - 14
U15 = -3


Moga membantu....