Question

Tentukan banyaknya suku barisan aritmetika berikut ; a=19, b= -5, dan Un = -41

Answer 1

Un = a + (n - 1) b
-41= 19 + (n - 1) -5
-41= 19 -5n + 5
5n = 24 + 41
n  = 65 ÷ 5
n = 13

Answer 2

Dik : a=19
b=5
un= -41

dij :

Un = a+(n-1)b
u-41 = 19 + (n-1) 5
-41 = 19 + 5n-5
-5n= 19 -5 + 41
-5n = 55
n = 55/-5
n = 11

Sn = n/2 ( U1 + Un)
= 11/2 (19 + (-41)
= 5.5 (-22)
= -121