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Yesika
Yesika asked in Sains & MatematikaMatematika · 7 years ago

Diketahui barisan aritmatika dengan suku ke-6= -7 dan suku ke-2 = 5. suku ke-30 barisan yg bersesuain adalah?

2 Answers

Rating
  • ?
    Lv 6
    7 years ago
    Favorite Answer

    rumus umum :

    Un = a + (n-1)b

    U6 = a + (6-1)b = -7 ---> U7 = a + 5b = -7

    U2 = a + (2-1)b = 5 ---> U2 = a + 1b = 5

    eliminasi :

    a + 5b = -7

    a + 1b = 5

    __________ -

    4b = -12

    b = -12/4

    b = -3

    substitusi b ke salah satu persamaan :

    a + 5b = -7

    a + 5(-3) = -7

    a - 15 = -7

    a = -7 + 15

    a = 8

    *mencari suku ke-30

    U30 = a + (n-1)b

    U30 = 8 + (30-1)-3

    U30 = 8+ (29)-3

    U30 = 8 - 87

    U30 = -29

    jadi suku ke-30 adalah -79

    Source(s): Hitungan sendiri
  • salcomp
    Lv 7
    7 years ago

    U6 - U2 = 4b

    -7 - 5 = 4b

    b = -12/4 = -3

    U30 = U6 + 24b

    U30 = -7 + 24(-3) = -79

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