Matematika

Pertanyaan

U3 = 9. U8 = 4. Tentukan U20

2 Jawaban

  • Materi : Barisan dan Deret
    Kelas : IX SMP

    U3 = U1 + 2b = 9
    U8 = U1 + 7b = 4
    -----------------------
    ⇒⇒⇒⇒⇒ -5b = 5
    ⇒⇒⇒⇒⇒ b = -1

    U3 = U1 + 2b
    9 = U1 + 2(-1)
    9 = U1 - 2
    U1 = 9 + 2
    U1 = 11

    U20 = U1 + 19b
    U20 = 11 + 19(-1)
    U20 = 11 - 19
    U20 = -8
  • U3 = 9
    a + 2b = 9 . . . (i)

    U8 = 4
    a + 7b = 4 . . . (ii)

    (i) & (ii)
    a + 2b = 9
    a + 7b = 4
    -------------- -
    -5b = 5
    b = -1

    a + 2b = 9
    a + 2(-1) = 9
    a - 2 = 9
    a = 11

    U20 = a + 19b = 11 + 19(-1) = 11 - 19 = -8

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