Đáp án:
`x=-721`
Giải thích các bước giải:
`(x+721)/2020+(x+21)/700+(x+721)/2001=-1`
`\to (x+721)/2020+(x+21)/700+(x+721)/2001+1=0`
`\to (x+721)/2020+((x+21)/700+1)+(x+721)/2001=0`
`\to (x+721)/2020+(x+21+700)/700+(x+721)/2001=0`
`\to (x+721)/2020+(x+721)/700+(x+721)/2001=0`
`\to (x+721)(1/2020+1/700+1/2001)=0`
Vì `1/2020+1/700+1/2001\ne0`
`\to x+721=0`
`\to x=-721`
Vậy `x=-721`
