Ta có:
` A = \frac{2020^{2018}-1}{2020^{2019}-2019} `
` <=> 2020A = \frac{2020^{2019} - 2020}{2020^{2019} - 2019} `
` B = \frac{2020^{2019}-1}{2020^{2020}+2019} `
` <=> 2020B = \frac{2020^{2020}-2020}{2020^{2020}+2019} `
Do: ` 2020^{2019} - 2019 < 2020^{2020} + 2019 `
` => \frac{2020^{2019} - 2020}{2020^{2019} - 2019} > \frac{2020^{2020}-2020}{2020^{2020}+2019} `
` => 2020A > 2020B `
` => A > B `