Tentukan nilai k agar bilangan-bilangan berikut membentuk barisan aritmatika K - 6, k - 1, 2k - 4, dan 3k - 7

U4 = k-6 + (3) × (k-1-k-6)
3k-7 = k-6 + (3) × (k-k-6-1)
3k-7 = k-6 + (3) × (5)
3k-7 = k-6 + (15)
3k-7 - k-6 = 15
3k-k - 7-6 = 15
2k - 13 = 15
2k = 15+13
2k = 28
k = 14

*)pembuktian :
k - 6 = 14-6 = 8
k - 1 = 14-1 = 13
2k-4 = (2×14)-4 = 28-4 = 24
3k-7 = (3×14)-7 = 32-7 = 25

b= 13-8 = 5

semoga membantu... ^.^