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Active Calculus 2nd Ed

Activity 3.6.5.
Consider the region in the \(x\)-\(y\) plane that is bounded by the \(x\)-axis and the function \(f(x) = 25-x^2\text{.}\) Construct a rectangle whose base lies on the \(x\)-axis and is centered at the origin, and whose sides extend vertically until they intersect the curve \(y = 25-x^2\text{.}\) Which such rectangle has the maximum possible area? Which such rectangle has the greatest perimeter?
(Challenge: answer the same questions in terms of positive parameters \(a\) and \(b\) for the function \(f(x) = b-ax^2\text{.}\))