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

Toán Lớp 8: Tìm x, biết:

Home/ Toán Lớp 8: Tìm x, biết:

Toán Lớp 8: Tìm x, biết:

Tháng Chín 26, 2022 Toán học 1 Comment 0 views

Toán Lớp 8: Tìm x, biết:
a/ 5x ( x-1 ) = x-1 b/ 2 ( x+5 ) – x^2 – 5x = 0 c/ x^2 + 5x – 6 = 0 d/ ( 2x + 3 )^2 – 4 ( x+1 ) ( x-1 ) = 49 e/ x^3 + x^2 + x + 1 = 0 f/ x^3 – x^2 = 4x^2 – 8x + 4

Comments ( 1 )

  1. hienchaudiem
    hienchaudiem
    26 Tháng Chín, 2022 at 5:03 sáng
    Reply
    Giải đáp:
    a, 5x(x-1) = x-1
    ⇔ 5x = (x-1)/(x-1)
    ⇔ 5x = 1
    ⇔ x = 1/5
    b, 2(x+5) -x^2-5x = 0
    ⇔ 2(x+5)-(x^2+5x) = 0
    ⇔ 2(x+5)-x(x+5) = 0
    ⇔ (x+5)(x-2) = 0
    ⇔ \(\left[ \begin{array}{l}x-2 = 0\\x+5=0\end{array} \right.\)
    ⇔ \(\left[ \begin{array}{l}x=2\\x=-5\end{array} \right.\) 
    c, x^2 + 5x – 6 = 0
    ⇔ (x^2-x)+(6x-6) = 0
    ⇔ x(x-1)+6(x-1) = 0
    ⇔ (x-1)(x+6) = 0
    ⇔ \(\left[ \begin{array}{l}x-1=0\\x+6=0\end{array} \right.\) 
    ⇔ \(\left[ \begin{array}{l}x=1\\x=-6\end{array} \right.\) 
    d, (2x+3)^2 – 4(x+1)(x-1) = 49
    ⇔ 4x^2+12x+9-4(x^2-1) = 49
    ⇔ 4x^2+12x+9-4x^2+4 = 49
    ⇔ (4x^2-4x^2)+12x+(9+4) = 49
    ⇔ 12x+13 = 49
    ⇔ 12x = 36
    ⇔ x = 3
    e, x^3+x^2+x+1 = 0
    ⇔ (x^3+x^2)+(x+1) = 0
    ⇔ x^2(x+1)+(x+1) = 0
    ⇔ (x+1)(x^2+1) = 0
    ⇔ x+1 = 0
    ⇔ x = -1
    f, x^3-x^2 = 4x^2-8x+4
    ⇔ x^2(x-1) = 4(x^2-2x+1)
    ⇔ x^2(x-1) = 4(x-1)^2
    ⇔ x^2 = 4(x-1)
    ⇔ x^2 = 4x-4
    ⇔ x^2-4x+4 = 0
    ⇔ (x-2)^2 = 0
    ⇔ x-2 = 0
    ⇔ x = 2
     

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

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