\(A=2021-1021:\left(199-x\right)\)
\(\Leftrightarrow A=2021-\frac{1021}{199-x}\)
\(MinA\Leftrightarrow\frac{1021}{199-x}Max\Leftrightarrow199-xMin\Leftrightarrow199-x=1\Leftrightarrow x=199-1\Leftrightarrow x=198\)
Lúc này \(A=2021-1021=100\)
Vậy \(MinA=1000\Leftrightarrow x=198\)