Minta tolong dong Deret aritmatika U2=4 S4=20 Tentukan nilai A, B dan S5

jawab

u2 =  4
a + b = 4 ....(i)

s4 =  20
4/2 ( 2a + 3b) = 20
2a + 3b = 10 ...(2)
 
a + b = 4.......(2)
2a + 3b = 10  

2a + 2b = 8
2a + 3b = 10

-b = - 2
b = 2

a + b = 4
a + 2 = 4
a = 2

s5 = 5/2 ( 2a + 4b)
s5  = 5/2 (4 + 8)
s5 = 5/2 (12)
s5 = 30