2.2. A farmer wants to enclose a rectangular plot of land with an electric fence 100 m long on three sides, the plot being located next to a river, so that the fence together with a section of the riverbank as the fourth side forms a rectangle. What should the dimensions of this rectangle be so that the area of the enclosed plot is maximized?
2.2. Let $BC$ be the side of the rectangle opposite the river. If $BC = x$, then $AB = CD = 50 - \frac{x}{2}$. The area of the rectangle is $P(x) = x\left(50 - \frac{x}{2}\right) = \frac{1}{2} x(100 - x)$. The maximum is reached at $x = 50$. Therefore, $AB = 25 \text{ m} = CD, BC = 50 \text{ m}$.