Suatu barisan aritmatika diketahui U2= 7 dan U6= 23. U40 barisan tersebut adalah.... Mohon penjelasannya...

Barisan Aritmetika

u2 = 7
u6 = 23

u6 - u2 = 23 - 7
(6-2)b = 16
4b = 16
b = 4

u40 = a + 39 b = a + 5b + 34 b
u40 = u6 + 34 b
u40 = 23 + 34(4)
u40 = 23 + 136
u40 = 159

U6 = 23
U2 = 7
U40 = ...

Un = a + (n-1) b
U6 = a + (6-1) b
23 = a + 5b ... Persamaan 1
U2 = a + (2-1) b
7 = a + 1b ... Persamaan 2

Eliminasi
23 = a + 5b
7 = a + 1b
------------------- -
16 = 4b
b = 16/4
= 4

Subtitusi

7 = a + 1b
7 = a + 1*4
a = 7-4
a = 3

Un = a + (n-1) b
U40 = 3 + (40-1) 4
U40 = 3 + 39*4
U40 = 3 + 156
U40 = 159