Dari barisan aritmatika suku ke 3=15 dan suku ke 8 =35. Suku ke 35 dari barisan tsb

a + 2b = 15
a + 7b = 35
------------------- -
5b = 20
b = 4

a + 2.4 = 15
a = 7

U35 = 7 + 34 . 4 = 7 + 136 = 143

----DERET ARITMATIKA----

U3 = U1 + 2b = 15
U8 = U1 + 7b = 35
----------------------------[-]
========> -5b = -20
========> b = 4

U3 = U1 + 2b
15 = U1 + 2(4)
15 = U1 + 8
U1 = 15 - 8
U1 = 7

Un = U1 + ( n-1) b
U35 = 7 + ( 35 -1) 4
U35 = 7 + 34.4
U35 = 7 + 136
U35 = 143

semoga membantu ^_^