最適化問題

The rod's maximum length is constrained by the tightest section of the corner it must navigate. Rather than directly maximizing rod length, the problem is reframed to minimize the clearance path at each angle. This minimum clearance represents the bottleneck that limits how long the rod can be. By identifying this critical constraint, you determine the longest rod that can successfully round the corner at any approach angle.

The rod length is divided into two components, L₁ and L₂, written using the hallway widths (3 meters and 2 meters) and trigonometric functions of the angle. The total length L combines these components based on how the rod touches the inner corner and extends to the outer walls. This angle-dependent expression allows you to analyze how length changes as the rod rotates through the corner.

Differentiation identifies where the slope of the length function equals zero, revealing the critical angle where clearance is minimized. Setting the derivative equal to zero and solving yields the angle that produces the bottleneck. This mathematical technique transforms the geometric problem into an algebraic one, enabling precise calculation of the optimal rod orientation.

The derivative equation contains secant and cosecant terms that are rewritten as sines and cosines. Rearranging terms to opposite sides groups the trigonometric functions, yielding a simplified expression involving tangent cubed. This algebraic manipulation makes the equation solvable, allowing you to isolate the critical angle value.

Substituting the critical angle into the original length equation provides the maximum length of the rod that can safely clear the corner. This final numerical result represents the longest horizontal pipe that can navigate the turn without vertical tilting. The calculation confirms that this length is indeed the limiting value across all possible approach angles.

The problem seeks to maximize rod length while constrained by the physical geometry of two perpendicular hallways. The constraint is that the rod must simultaneously clear both hallway walls at every angle. Optimization problems like this demonstrate how calculus identifies extreme values—maximum or minimum—within real-world physical or geometric boundaries.

By minimizing the clearance length function L(θ), you identify the angle where the corner is most restrictive. This minimum clearance directly determines the maximum rod length that works at all angles. The strategy of minimizing a constraint function rather than directly maximizing the desired quantity is a powerful technique in constrained optimization settings.