Question

Ditentukan deret aritmetika U1+U3=20 dan U5+U7=116.tentukan empat suku pertama deret tersebut...

Answer 1

Un = a+(n-1)b

U1 + U3 = 20
a + a + 2b = 20
2a + 2b = 20
a + b = 10 ... pers 1

U5 + U7 = 116
a + 4b + a + 6b = 116
2a + 10b = 116
a + 5b = 58 ... pers 2

eleminasi pers 1 dan 2
a + 5b = 58
a + b = 10 _
   4b  = 48
     b = 12

substitusi
a + b = 10
a + 12 = 10
a = 10 - 12
a = -2

U1 = a = -2
U2 = a + b = -2 + 12 = 10
U3 = a + 2b = -2 + 2(12) = -2 + 24 = 22
U4 = a + 3b = -2 + 3(12) = -2 + 36 = 34

semoga membantu ya :)