GIÚP MÌNH VỚI HWASVOTE 5 SAO x ³-27+4x ²-12=0 (2-x/2019)-1=(1-x/2020)-(x/2021)

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1. Giải thích các bước giải:

   a.Ta có:

   $x^3-27+4x^2-12=0$

   $\to x^3+4x^2-39=0$

   $\to x\approx \:2.45753\dots $

   b.Ta có:

   $\dfrac{2-x}{2019}-1=\dfrac{1-x}{2020}-\dfrac{x}{2021}$

   $\to \dfrac{2-x}{2019}+1=(\dfrac{1-x}{2020}+1)+(1-\dfrac{x}{2021})$

   $\to \dfrac{2-x+2019}{2019}=\dfrac{1-x+2020}{2020}+\dfrac{2021-x}{2021}$

   $\to \dfrac{2021-x}{2019}=\dfrac{2021-x}{2020}+\dfrac{2021-x}{2021}$

   $\to \dfrac{2021-x}{2019}-\dfrac{2021-x}{2020}-\dfrac{2021-x}{2021}=0$

   $\to (2021-x)(\dfrac{1}{2019}-\dfrac{1}{2020}-\dfrac{1}{2021})=0$

   $\to 2021-x=0$

   $\to x=2021$

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2. Đáp án+Giải thích các bước giải:

   1)`x ³-27+4x ²-12=0`

   `<=>x^3+4x^2-39=0`

   `<=> x\approx 2.45753…`

   ____________________________________

   `x ³-27+4x ²-12x=0`

   `<=>(x-3)(x^2+3x+9)+4x(x-3)=0`

   `<=>(x-3)(x^2+7x+9)=0`

   `<=>(x-3)(x^2+2.x. 7/2 +49/4-13/4)=0`

   `<=>(x-3)[(x+7/2)^2- “(frac{\sqrt13}{2})^2`

   `<=>(x-3)(x+7/2-\sqrt13 /2)(x+7/2+\sqrt13 /2)`

   `<=>x=3; x=-7/2+-\sqrt13 /2`

   Vậy `x=3; x=-7/2+-\sqrt13 /2`

   2) `(2-x)/2019-1=(1-x)/2020-x/2021`

   `<=>(2-x)/2019+1=(1-x)/2020+1-x/2021+1`

   `<=>(2021-x)/2019 = (2021-x)/2020 -(2021-x)/2021`

   `<=>(2021-x)/2019 – (2021-x)/2020 +(2021-x)/2021=0`

   `<=>(2021-x)(1/2019-1/2020+1/2021)=0`

   `<=>2021-x=0(vì 1/2019-1/2020+1/2021\ne 0)`

   `<=>x=2021`

   Vậy `x=2021`

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