` a) ` ` \frac{2017×2018+2019}{2018×2019-2017} `

` = \frac{2017×2018+(2018+1)}{2018×2019-(2018-1)} `

` = \frac{2017×2018+2018+1}{2018×2019-2018+1} `

` = \frac{2018×(2017+1)+1}{2018×(2019-1)+1} `

` = \frac{2018×2018+1}{2018×2018+1} `

` = 1 `

` b) ` ` \frac{637×527-189}{526×637+448} `

` = \frac{637×527-(637-448)}{526×637+448} `

` = \frac{637×527-637+448}{526×637+448} `

` = \frac{637×(527-1) + 448}{526×637+448} `

` = \frac{637×526+448}{526×637+448} `

` = 1 `

$a$)

Ta có:

$\dfrac{2017 \times 2018 + 2019}{2018 \times 2019 - 2017}$

$= \dfrac{2017 \times 2018 + 2019}{2018 \times 2017 + 2018 \times 2 - 2017}$

$= \dfrac{2017 \times 2018 + 2019}{2018 \times 2017 + 4036 - 2017}$

$= \dfrac{2017 \times 2018 + 2019}{2018 \times 2017 + 2019}$

$= 1$

$b$)

Ta có:

$\dfrac{637 \times 527 - 189}{526 \times 637 + 448}$

$= \dfrac{637 \times 527 + 637 - 189}{526 \times 637 + 448}$

$= \dfrac{637 \times 527 +448}{526 \times 637 + 448}$

$= 1$