Question

Mau tanya nomor 9 tolong dbantu beserta cara makasih

Answer 1

U3 = 14
a+2b = 14

U7 = 26
a+6b = 26

a+6b = 26
a+2b = 14 -
----------------
4b = 12
b = 12:4
b = 3

a+2b = 14
a+2.3 = 14
a+6 = 14
a = 14-6
a = 8

S18 = n/2.(2a+(n-1).b)
S18 = 18/2.(2.8+(18-1).3)
S18 = 9.(16+17.3)
S18 = 9.(16+51)
S18 = 9.67
S18 = 603

Jawaban: B

Answer 2

Caranya,
pertama cari bedanya dulu
U7 = 26
U3 = 14

7-3 <--> 26-14
= 4 = 12
b = 12 ÷ 4
= 3

trus cari U1
Un = a+(n-1)b
U3 = a+(3-1)3
14 = a+(2)3
a = 6-14
= 8

habis itu, cari U18
U18 = 8+(18-1)3
= 8+(17)3
= 8+51
= 59

terakhir yg ditanya S18
Sn = n/2 (a+Un)
= 18/2 (8+59)
= 9 (67)
= 603

jadi, jawabannya B
makasi,moga paham + bantu :))