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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 8: Bài 2: Tìm x, biết: a) 9×2 – 49 = 0 b) (x + 3)(x2 – 3x + 9) –x(x – 1)(x + 1) – 27 = 0 c)(x – 1)(x + 2) = x + 2 d) x(3x + 2) + (x + 1

Toán Lớp 8: Bài 2: Tìm x, biết:
a) 9×2 – 49 = 0 b) (x + 3)(x2 – 3x + 9) –x(x – 1)(x + 1) – 27 = 0
c)(x – 1)(x + 2) = x + 2 d) x(3x + 2) + (x + 1)2 – (2x – 5)(2x + 5) = 0

Comments ( 1 )

  1. Giải đáp +Lời giải và giải thích chi tiết:
     a) 9x^2 – 49 = 0
    ⇔ (3x)^2 – 7^2 = 0
    ⇔ (3x-7) (3x+7) = 0
    +) 3x – 7 = 0
    ⇔ 3x = 7
    ⇔ x = 7/3
    +) 3x + 7 = 0
    ⇔ 3x = -7
    ⇔ x = -7/3
    Vậy x = +- 7/3
    b) (x+3) (x^2-3x+9) – x (x-1) (x+1) – 27 = 0
    ⇔ x^3 + 27 – x (x^2-1) – 27 = 0
    ⇔ x^3 – x^3 + x = 0
    ⇔ x = 0
    Vậy x = 0
    c) (x-1) (x+2) = x + 2
    ⇔ x^2 + 2x – x – 2 – x – 2 = 0
    ⇔ x^2 – 4 = 0
    ⇔ x^2 = 4
    ⇔ x = +- 2
    Vậy x = +- 2
    d) x (3x+2) + (x+1)^2 – (2x-5) (2x+5) = 0
    ⇔ 3x^2 + 2x + x^2 + 2x + 1 – 4x^2 + 25 = 0
    ⇔ 4x + 26 = 0
    ⇔ 4x = -26
    ⇔ x = -26 : 4
    ⇔ x = -13/2
    Vậy x = -13/2

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222-9+11+12:2*14+14 = ? ( )