Question

Sebuah bilangan aritmatika 19,14,9,4,.. Tentukanlah:
a. Suku ke 31
b. Jumlah 13 suku pertama

Answer 1

Verified answer

U1= 19
u2= 14
b= u2-u1
= 14-19
= -5

un= a+(n-1)b
un= 19+(n-1)(-5)
un= -5n+5+19
un= -5n+24

u31= -5(31)+24
u31= -155+24
u31= -131

sn= n/2(2.a+(n-1)b)
s13= 13/2(2(19)+(13-1)(-5)
s13= 13/2(38+(12)(-5)
s13= 13/2(38-60)
s13= 13/2(-22)
s13= 13(-11)
s13= -143

Answer 2

A. Un = a +(n - 1 ) b
U31= 19 + ( 31 - 1 ) -5
= 19 + 30 × -5
= 19 + (-150 )
= -131
smg membantu