Câu 13 .
$\frac{x+2019}{x+2018}$ $=$$\frac{4038}{4037}$
$\frac{x+2018+1}{x+2018}$ $=$ $\frac{4037+1}{4037}$
$1$ $+$ $\frac{1}{x+2018}$ $=$ $1$ $+$ $\frac{1}{4037}$
$\frac{1}{x+2018}$ $=$ $\frac{1}{4037}$
$x$ $+$ $2018$ $=$ $4037$
$x$ $=$ $4037$ $-$ $2018$ $x$ $=$ $2019$
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