Question

Diketahui barisan aritmatika 35,31,27,23... tentukan
a. suku ke-n
b. suku ke-50
c. jumlah 20 suku pertamanya

Answer 1

35, 31 ,27,23, ...
a = 35
b = 31 - 35 = -4

a) Un = a + (n-1) b
Un = 35 + (n-1) (-4)
Un = 35 -4n + 4
Un = -4n + 39

b) U50 = -4(50) + 39
= -200 + 39
= -161

c) Sn = n/2 (2.a + (n-1) b)
S20 = 20/2 (2.35 + (20-1) (-4) )
= 20/2 (70 + (19) (-4) )
=20/2 (70 + (-76) )
=20/2 ( -6)
= -60

maap klo salah