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

Toán Lớp 8: `(x+1)^3-(x-1)^3-6(x-1)^2= -19`

Tháng Tám 28, 2022 Toán học 2 Comments 0 views

Toán Lớp 8: (x+1)^3-(x-1)^3-6(x-1)^2= -19

Comments ( 2 )

  1. haiyemy
    haiyemy
    28 Tháng Tám, 2022 at 12:10 sáng
    Reply
    Gửi bạn:
    $(x+1)^3-(x-1)^3-6(x-1)^2=-19$
    $x^3+3x^2+3x+1-(x^3-3x^2+3x-1)-6(x^2-2x+1)=-19$
    $x^3+3x^2+3x+1-x^3+3x^2-3x+1-6x^2+12x-6=-19$
    $12x-4=-19$
    $12x=-19+4$
    $12x=-15$
    $x=\dfrac{-15}{12}=\dfrac{-5}{4}$

  2. kymmailien
    kymmailien
    28 Tháng Tám, 2022 at 12:10 sáng
    Reply
    Giải đáp:
     $(x+1)³-(x-1)³-6.(x-1)²=-19$
    $⇔ x³+3x²+3x+1-x³+3x²-3x+1-6.(x²-2x+1)=-19$
    $⇔ x³+3x²+3x+1-x³+3x²-3x+1-6x²+12x-6=-19$
    $⇔ (x³-x³)+(3x²+3x²-6x²)+(3x-3x+12x)+(1+1-6)=-19$
    $⇔ 12x-4=-19$
    $⇔ 12x= -15$
    $⇔ x=-\dfrac{15}{12}$
    $⇔ x=-\dfrac{5}{4}$
    $vậy$ $x=-\dfrac{5}{4}$
     

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

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