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...`
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`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`
