Matematika

Pertanyaan

tentukan jumlah 9 suku pertama dari deret 160 + 80 + 40 + 20 + ....

1 Jawaban

  • a = 160
    r = U2/U1 = 80/160 = 1/2

    Sn = a ( 1 - r^n ) / 1 - r
    S9 = 160 ( 1 - 1/2^9 ) / 1 - 1/2
    S9 = 160 ( 1 - 1/512 ) / 1/2
    S9 = 320 ( 1 - 1/512)
    S9 = 320 - 320/512
    S9 = (2^5)(10) - (2^5)(10)/(2^9)
    S9 = (2^5)(10) - 10/2^4
    S9 = [(2^9)(10) - 10] / 2^4
    S9 = 5120 - 10 / 16
    S9 = 5110 / 16
    S9 = 2555 / 8

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