tentukan suku ke 18
2. diketahui U5 dan U8 barisan aritmatika
adalah 42 dan 36. tentukan U20!
mohon bantuannya soal Ny besok
dikumpulkan
1. 28, 24, 20= ……
-Barisan dan deret-
1) . 28, 24, 20,…
a = 28
b = 24 – 28
b = -4
Un = a + (n – 1) b
U18 = 28 + (18 – 1) -4
U18 = 28 + (17 × (-4))
U18 = 28 + (-68)
U18 = -40
===============
2). U5 = 42
U8 = 36
U5 = a + 4b = 42
U8 = a + 7b = 36
———————– (-)
-3b = 6
b = -2
a + 4b = 42
a + 4 (-2) = 42
a + (-8) = 42
a = 42 + 8
a= 50
Suku ke – 20
Un = a + (n – 1) b
U20 = 50 + (20 – 1) -2
U20 = 50 + (19 × (-2))
U20 = 50 + (-38)
U20 = 12