Diketahui suatu barisan Aritmatika U8-U10 + U₁₂-U14+ U16 = 49 dan U₂=9. maka Tentukan S29?
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Penjelasan dengan langkah-langkah:
Un = a + ( n - 1 ) b
U2 = a + b
U8 = a + 7b
U10 = a + 9b
U12 = a + 11b
U14 = a + 13b
U16 = a + 15b
Dan
U2 = 9
U8 - U10 + U12 - U14 + U16 = 49
Sehingga diperoleh,
a + b = 9 ------ (1)
a + 7b - (a + 9b) + a + 11b - (a + 13b) + a + 15b = 49
-2b - 2b + a + 15b = 49
a + 11b = 49 ------- (2)
a + b = 9
a + 11b = 49
------------------- (-)
-10b = - 40
b = 4
Maka,
a + 4 = 9
a = 5
U29 = a + 28b = 5 + 4 x 28 = 117
Maka,