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deret aritmatik :
2,5 + 3,5 + 4,5 +... 97,5
a = 2,5
b = U2-U1 = 3,5 - 2,5 = 1
Dit : Sn?
Jawab :
Pertama-tama, cari dulu banyak 'n' nya (gunakan Un dari suku terakhir)
Un = a+(n-1)b
97,5 = 2,5 + (n-1) 1
97,5 = 2,5 + 1n - 1
97,5 - 2,5 + 1 = 1n
96 = n <======
Sn = n/2 (2a+(n-1)b)
S96 = 96/2 (2 . 2,5 + (96-1) 1)
S96 = 48 (5 + 95 .1)
S96 = 48(100)
S96 = 4800 <======= jumlah dari deret bilangan