diketahui barisan aritmarika ke-6=7 dan suku ke-3=16 tentukan suku ke-8 barisan tersebut

Un = a + ( n - 1 ) b

U6 = a + 5b = 7
U3 = a + 2b = 16
-------------------------(-)
3b = - 9
b = - 3

a + 2b = 16
a + 2(-3) = 16
a - 6 = 16
a = 16 + 6
a = 22

U8 = a + 7b
= 22 + 7(-3)
= 22 - 21
= 1

Un = a + (n - 1)b

U6 = a + 5b = 7
U3 = a + 2b = 16
_____________ _
3b = -9
b = -9/3
b = -3

a + 2b = 16
a + 2.(-3) = 16
a - 6 = 16
a = 16 + 6
a = 22

Maka,
Un = a + (n - 1)b
U8 = 22 + (8 - 1).(-3)
U8 = 22 + 7.(-3)
U8 = 22 - 21
U8 = 1

Semoga membantu dan semoga bermanfaat...