\[\boxed{\text{560.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[І\ способ.\]
\[P = 62\ м;\ \ S = 210\ м^{2}\]
\[P = (a + b) \cdot 2 = 62\ м\]
\[S = ab = 210\ м^{2}\]
\[(31 - b)b = 210\]
\[31b - b^{2} - 210 = 0\]
\[b^{2} - 31b + 210 = 0\]
\[D = 961 - 840 = 121\]
\[b_{1,2} = \frac{31 \pm \sqrt{121}}{2} = \frac{31 \pm 11}{2}\]
\[b_{1} = 10\ м\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ b_{2} = 21\ м\]
\[a_{1} = 31 - b_{1}\text{\ \ \ \ \ \ \ \ \ \ }a_{2} = 31 - b_{2}\]
\[a_{1} = 31 - 10 = 21\ м\]
\[a_{2} = 31 - 21 = 10\ м\]
\[ІІ\ способ.\]
\[Пусть\ одна\ сторона\ \]
\[прямоугольника\ \text{x\ }м,\ тогда\ \]
\[вторая\ сторона\ равна:\]
\[62\ :2 - x = (31 - x)\ м.\]
\[Площадь\ прямоугольника\ по\ \]
\[условию\ равна\ 210\ м^{2}.\]
\[Составим\ уравнение:\]
\[x(31 - x) = 210\]
\[31x - x^{2} = 210\ \ \ \ \ \ \ | \cdot ( - 1)\]
\[x^{2} - 31x + 210 = 0\]
\[D = 961 - 840 = 121\]
\[x_{1} = \frac{31 + 11}{2} = \frac{42}{2} = 21\ (м);\ \]
\[\text{\ \ }x_{2} = \frac{31 - 11}{2} = \frac{20}{2} = 10\ (м).\]
\[31 - x = 31 - 10 = 21\ (м).\]
\[31 - x = 31 - 21 = 10\ (м).\]
\[Ответ:21\ м\ и\ 10\ м\ или\ 10\ м\ и\ \]
\[21\ м.\ \]