She pulled a chair, settled into the worn leather, and spread out her notes. The room was quiet except for the distant hum of the campus heating system and the occasional rustle of a late‑night janitor’s cart. Maya began by sketching the situation on a scrap of graph paper. A sphere centered at the origin, radius R , and a rectangular box whose center coincided with the sphere’s center. Because the base was a square, she let x denote the length of one side of the base, and y the height of the box.
Finally, the maximal volume:
Maya solved for in terms of x :
The vertices of the box lie on the sphere, so each corner satisfies the equation
She felt a surge of satisfaction. The problem had been reduced to a single‑variable function, exactly as the title promised. The next step was to find the maximum of (V(x)). Maya knew she needed the derivative (V'(x)) and the critical points where it vanished (or where the derivative was undefined). She set her mind to the task. She pulled a chair, settled into the worn
Plugging this back into the expression for :
First, she rewrote the volume in a friendlier form for differentiation: A sphere centered at the origin, radius R
After the class, several classmates gathered around Maya, peppering her with questions. She explained how the symmetry of the sphere forced the optimal box to be a cube, and how the derivative’s denominator reminded her to stay within the physically meaningful interval (0 < x < \sqrt{2},R). Later that night, Maya returned the Thomas & Finney volume to its shelf, the thin solution sheet now neatly folded back into place. She closed the library’s heavy door and stepped into the cool campus air, the bell of the clock tower echoing the rhythm of her thoughts.
[ V(x) = 2x^2 \bigl(R^2 - \tfrac{x^2}{2}\bigr)^{1/2}. ] The problem had been reduced to a single‑variable
[ V(x) = x^2 \cdot y = x^2 \cdot 2\sqrt{R^2 - \frac{x^2}{2}} = 2x^2\sqrt{R^2 - \frac{x^2}{2}} . ]