Barisan aritmatika U4=9 U9=19 U30? Bantu jawab pake rumus please

Un = a + ( n - 1 ) b

eliminasi

U4 = a + 3b = 9
U9 = a + 8b = 19
------------------------ (-)
-5b = -10
b = -10 ÷ -5
b = 2

subtitusi
a + 3b = 9
a + 3 × 2 = 9
a + 6 = 9
a = 9 - 6
a = 3

U30 = 3 + 29 × 2
U30 = 3 + 58
U30 = 61

¶ U4 = 9
¶ U9 = 19

Ditanya U30

Jawab

Rumus deret aritmatika adalah
Un = a + (n-1)b

Maka:
U4 = a + 3b
9 = a + 3b Pers. 1

U9 = a + 8b
19 = a + 8b Pers. 2

¶Persamaab 1 dan 2 dieliminasi

a + 3b = 9
a + 8b = 19
,…………. ….. — pengurangan
-5b = -10
b = 2

Nilai a dapat dicari:

a + 3b = 9
a + 3(2)=9
a = 9 - 6
a = 3

Maka U30??

U30= a + (n-1)b
U30= 3 + (29)(2)
U30= 3 + 58
U30 = 61