diketahui deret aritmatika 8,19/3,14/3,3,.. tentukan a. a,b, dan Sn b.U12 c.S12

a.) a = 8
b = 19/3 - 8
= 19/3 - 24/3
= -5/3
Sn = 1/2(2a + (n - 1)b)
= 1/2(2(8) + (n - 1)(-5/3))
= 1/2(16 -(5/3)n + 5/3)
Sn = 8 + 1/2((-5/3)n + 5/3)

b.) U12 = a + 11b
U12 = 8 + 11(-5/3)
U12 = 8 -55/3
U12 = 24/3 -55/3
U12 = -31/3

c.) S12 = 8 + 1/2((-5/3)12 + 5/3)
S12 = 8 + 1/2(-20 + 5/3)
S12 = 8 + 1/2(-60/3 + 5/3)
S12 = 8 + 1/2(-55/3)
S12 = 8 - 55/6
S12 = 48/6 - 55/6
S12 = -7/6