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

Toán Lớp 8: Bài 1: Tìm x biết: 1, (x-3)(x^2+3x+9)+x(x+2)(2-x)=1 2,(x+1)^3-(x-1)^3-6(x-1)^2=-10 3,(x-1)(x^2+x+1)-x(x-2)(x+2)=5 4,x^3_27x-9x^2-27=0 5

Tháng Hai 2, 2023 Toán học 2 Comments 0 views

Toán Lớp 8: Bài 1: Tìm x biết:
1, (x-3)(x^2+3x+9)+x(x+2)(2-x)=1
2,(x+1)^3-(x-1)^3-6(x-1)^2=-10
3,(x-1)(x^2+x+1)-x(x-2)(x+2)=5
4,x^3_27x-9x^2-27=0
5,x^3+6x^2+12x+8=0
6,(x-1)^3-(x+3)(x^2-3x+9)+3(x^2-4)=2
giải nhanh giúp mình nha, mình cần gấp!!!!

Comments ( 2 )

  1. dantam45
    dantam45
    2 Tháng Hai, 2023 at 11:46 chiều
    Reply
    1)(x-3)(x²+3x+9)+x(x+2)(2-x)=1
    ⇔x³-27+x(2+x)(2-x)=1
    ⇔x³-27+x(4-x²)=1
    ⇔x³-27+4x-x³=1
    ⇔4x-27=1
    ⇔4x=1+27
    ⇔4x=28
    ⇔x=28:4
    ⇔x=7
    Vậy x=7
    2)(x+1)³-(x-1)³-6(x-1)²=-10
    ⇔x³+3x²+3x+1-(x³-3x²+3x-1)-6(x²-2x+1)=-10
    ⇔x³+3x²+3x+1-x³+3x²-3x+1-6x²+12x-6=-10
    ⇔(x³-x³)+(3x²+3x²-6x²)+(3x-3x+12x)+(1+1-6)=-10
    ⇔12x-4=-10
    ⇔12x=-10+4
    ⇔12x=-6
    ⇔x=-6/12
    ⇔x=-1/2
    Vậy x=-1/2
    3)(x-1)(x²+x+1)-x(x-2)(x+2)=5
    ⇔x³-1-x(x²-4)=5
    ⇔x³-1-x³+4x=5
    ⇔4x-1=5
    ⇔4x=5+1
    ⇔4x=6
    ⇔x=6/4
    ⇔x=3/2
    Vậy x=3/2
    4) Sửa đề:x³-27x-9x²-27=0
    →x³+27x-9x²-27=0
    ⇔x³-9x²+27x-27=0
    ⇔x³-3.x².3+3.x.3²-3³=0
    ⇔(x-3)³=0
    ⇔x-3=0
    ⇔x=3
    Vậy x=3
    5)x³+6x²+12x+8=0
    ⇔x³+3.x².2+3.x.2²+2³=0
    ⇔(x+2)³=0
    ⇔x+2=0
    ⇔x=-2
    Vậy x=-2
    6)(x-1)³-(x+3)(x²-3x+9)+3(x²-4)=2
    ⇔x³-3x²+3x-1-(x³+27)+3x²-12=2
    ⇔x³-3x²+3x-1-x³-27+3x²-12=2
    ⇔(x³-x³)+(-3x²+3x²)+3x-(1+27+12)=2
    ⇔3x-40=2
    ⇔3x=2+40
    ⇔3x=42
    ⇔x=42:3
    ⇔x=14
    Vậy x=14

  2. annhocbichchaubich
    annhocbichchaubich
    2 Tháng Hai, 2023 at 11:46 chiều
    Reply
    Giải đáp + giải thích các bước giải:
    1) (x-3)(x^2+3x+9)+x(x+2)(2-x)=1
    ->x^3-27-x(x+2)(x-2)=1
    ->x^3-27-x(x^2-4)=1
    ->x^3-27-x^3+4x=1
    ->4x-27=1
    ->4x=28
    ->x=7
    Vậy S={7}
    2) (x+1)^3-(x-1)^3-6(x-1)^2=-10
    ->[(x+1)-(x-1)][(x+1)^2+(x+1)(x-1)+(x-1)^2]-6(x-1)^2=-10
    ->2(x^2+2x+1+x^2-1+x^2-2x+1)-6(x^2-2x+1)=-10
    ->2(3x^2+1)-6x^2+12x-6=-10
    ->6x^2+2-6x^2+12x=-4
    ->12x=-6
    ->x=-1/2
    Vậy S={-1/2}
    3) (x-1)(x^2+x+1)-x(x-2)(x+2)=5
    ->x^3-1-x(x^2-4)=5
    ->x^3-1-x^3+4x=5
    ->4x=6
    ->x=3/2
    Vậy S={3/2}
    4) Sửa đề: x^3-9x^2+27x-27=0
    ->x^3-3.3.x^2+3.x.3^2-3^3=0
    ->(x-3)^3=0
    ->x-3=0
    ->x=3
    Vậy S={3}
    5) x^3+6x^2+12x+8=0
    ->x^3+3.2.x^2+3.x.2^2+2^3=0
    ->(x+2)^3=0
    ->x+2=0
    ->x=-2
    Vậy S={-2}
    6) (x-1)^3-(x+3)(x^2-3x+9)+3(x^2-4)=2
    ->x^3-3x^2+3x-1-x^3-27+3x^2-12=2
    ->3x-40=2
    ->3x=42
    ->x=14
    Vậy S={14}

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

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