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

Toán Lớp 8: Tìm x, biết: a) 3×2 (2x -7) + (2 – x) (6×2 – x + 3) + 8×2 = 4x – 2 b) 6×2 – (2x + 5) – (3x – 2) = 7 c) x (x – 5) (x + 5) – (x + 2) (

Tháng Một 8, 2023 Toán học 1 Comment 0 views

Toán Lớp 8: Tìm x, biết:
a) 3×2 (2x -7) + (2 – x) (6×2 – x + 3) + 8×2 = 4x – 2
b) 6×2 – (2x + 5) – (3x – 2) = 7
c) x (x – 5) (x + 5) – (x + 2) (x2 – 2x + 4) =17

Comments ( 1 )

  1. lanminhngoc
    lanminhngoc
    8 Tháng Một, 2023 at 3:57 chiều
    Reply
    Giải đáp:
    a)x=8/9
    b)x∈{$\dfrac{\sqrt[]{265}+5}{12}$;$\dfrac{5-\sqrt[]{265}}{12}$}
    c)x=-1
    Lời giải và giải thích chi tiết:
    a)3x²(2x-7)+(2-x)(6x²-x+3)+8x²=4x-2
    ⇔6x³-21x²+12x²-2x+6-6x³+x²-3x+8x²=4x-2
    ⇔(6x³-6x³)+(-21x²+12x²+x²+8x²)+(-2x-3x)+6=4x-2
    ⇔-5x+6=4x-2
    ⇔-5x-4x=-2-6
    ⇔-9x=-8
    ⇔x=8/9
    Vậy x=8/9
    b)6x²-(2x+5)-(3x-2)=7
    ⇔6x²-2x-5-3x+2=7
    ⇔6x²-(2x+3x)-(5-2)=7
    ⇔6x²-5x-3=7
    ⇔6x²-5x-3-7=0
    ⇔6x²-5x-10=0
    ⇔6(x²-5/6x-5/3)=0
    ⇔6(x²-5/6x+25/144-265/144)=0
    ⇔6(x²-5/6x+25/144)-265/24=0
    ⇔6[x²-2.x. 5/12+(5/12)^2]=265/24
    ⇔6(x-5/12)^2=265/24
    ⇔(x-5/12)^2=265/24:6
    ⇔(x-5/12)^2=265/24 . 1/6
    ⇔(x-5/12)^2=265/144
    ⇔(x-5/12)^2=($\dfrac{\sqrt[]{265}}{12}$)^2
    ⇔$\left[\begin{matrix} x-\dfrac{5}{12}=\dfrac{\sqrt[]{265}}{12}\\ x-\dfrac{5}{12}=-\dfrac{\sqrt[]{265}}{12}\end{matrix}\right.$
    ⇔$\left[\begin{matrix} x=\dfrac{\sqrt[]{265}}{12}+\dfrac{5}{12}\\ x=-\dfrac{\sqrt[]{265}}{12}+\dfrac{5}{12}\end{matrix}\right.$
    ⇔$\left[\begin{matrix} x=\dfrac{\sqrt[]{265}+5}{12}\\ x=\dfrac{5-\sqrt[]{265}}{12}\end{matrix}\right.$
    Vậy x∈{$\dfrac{\sqrt[]{265}+5}{12}$;$\dfrac{5-\sqrt[]{265}}{12}$}
    c)x(x-5)(x+5)-(x+2)(x²-2x+4)=17
    ⇔x(x²-25)-(x³+8)=17
    ⇔x³-25x-x³-8=17
    ⇔-25x-8=17
    ⇔-25x=17+8
    ⇔-25x=25
    ⇔x=25:(-25)
    ⇔x=-1
    Vậy x=-1

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

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