giúp e với mn nhanh nha 5* + tim và câu tlhn

`***`$\color{#1c1c1c}{\text{t}}$$\color{#363636}{\text{r}}$$\color{#4f4f4f}{\text{u}}$$\color{#696969}{\text{m}}$$\color{#828282}{\text{t}}$$\color{#9c9c9c}{\text{td}}$

`(x-2)^3-(x-9)^3=21(x-8)^2`

`x^3-6x^2+12x-8-x^3+27x^2-243x+729=21(x^2-16x+64)`

`21x^2-231x+721=21x^2-336x+1344`

`21x^2-231x=21x^2-336x+623`

`21x^2-231x-(21x^2-336x)=21x^2-336x+623-(21x^2-336x)`

`105x=623`

`x=\frac{89}{15}`

Vậy `x=89/15`

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`(5x-6)^2-(3x-7)^2=-9x(x-8)+(5x-6)^2-13`

`(5x-6)^2-(3x-7)^2-(5x-6)^2=-9x(x-8)+(5x-6)^2-13-(5x-6)^2`

`-(3x-7)^2=-9x(x-8)-13`

`-9x^2+42x-49=-9x^2+72x-13`

`-9x^2+42x=-9x^2+72x+36`

`-9x^2+42x-(-9x^2+72x)=-9x^2+72x+36-(-9x^2+72x)`

`-30x=36`

`x=-\frac{6}{5}`

Vậy `x=-6/5`