• Tìm `x` biết: `x + 721/2020“+“x + 21/700“+“x + 721/2021“=“- 1` Giúp mị với-???? Camon ạ:3

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1. `(x + 721)/2020 + (x + 21)/700 + (x + 721)/2021 = -1`

   `=> (x + 721)/2020 + (x + 21)/700 + (x + 721)/2021 + 1 = -1 + 1`

   `=> (x + 721)/2020 + (x + 21)/700 + (x + 721)/2021 + 1 = 0`

   `=> (x + 721)/2020 + (x + 21)/700 + (x + 721)/2021 + 700/700 = 0`

   `=> (x + 721)/2020 + (x + 21 + 700)/700 + (x + 721)/2021 = 0`

   `=> (x + 721)/2020 + (x + 721)/700 + (x + 721)/2021 = 0`

   `=> (x + 721) . (1/2020 + 1/700 + 1/2021) = 0`

   `=>` \(\left[ \begin{array}{l}x + 721 = 0\\\dfrac{1}{2020} + \dfrac{1}{700} + \dfrac{1}{2021} = 0\end{array} \right.\) 

   Mà `1/2020 + 1/700 + 1/2021 \ne 0`

   `=> x + 721 = 0`

   `=> x = 0 – 721`

   `=> x = -721`

   Vậy `x = -721`

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2. `(x+721)/2020+(x+21)/700+(x+721)/2021=-1`

   `⇔(x+721)/2020+(x+21)/700+(x+721)/2021+1=-1+1`

   `⇔(x+721)/2020+(x+21)/700+(x+721)/2021+700/700=0`

   `⇔(x+721)/2020+(x+21+700)/700+(x+721)/2021=0`

   `⇔(x+721)/2020+(x+721)/700+(x+721)/2021=0`

   `⇔(x+721).(1/2020+1/700+1/2021)=0`

   `⇔`\(\left[ \begin{array}{l}x+721=0\\\dfrac{1}{2020}+\dfrac{1}{700}+\dfrac{1}{2021}=0\end{array} \right.\) 

   Mà `(1/2020+1/700+1/2021)\ne0`

   `⇔x+721=0`

   `⇔x=-721`

   Vậy `x=-721.`

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