MHB Express rectangle area as function of x

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The area A of the rectangle can be expressed as A = x(36 - x^2), where x is the length along the x-axis and the height is determined by the graph y = 36 - x^2. The domain of A is 0 ≤ x ≤ 6, as the rectangle's corners must remain within the first quadrant. To find the maximum area, the function A can be analyzed using calculus, revealing that A is largest when x = 3. The maximum area occurs at this value, providing a clear solution to the problem.
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Hey so another expressing functions question:

A rectangle has on corner on the graph of y=36-x^2, another at the origin, a 3rd on the positive y-axis, and the fourth on the positive x-axis. Express the area A of the rectangle as a function of x. What is the domain of A? For what value of x is A largest?
 
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Let's look at a diagram:

View attachment 2132

In terms of $x$, what is the base of the rectangle...what is its height?
 

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