Câu 8
`A = \frac{2}{2018 \times 2020} + \frac{2021}{2020} - \frac{2019}{2018}`
`A = \frac{1}{2018} - \frac{1}{2020} + \frac{2021}{2020} - \frac{2019}{2018}`
`A = ( \frac{1}{2018} - \frac{2019}{2018} ) + ( \frac{2021}{2020} - \frac{1}{2020} )`
`A = ( -1 ) + 1`
`A = 0`