Let the length of the rectangle be $y$ feet. Then, by the Pythagorean theorem, we have $x^2 + y^2 = (2 \cdot 8)^2 = 256$. Solving for $y$, we get $y = \sqrt{256 - x^2}$. The area of the rectangle is given by $A(x) = x \cdot y = x\sqrt{256 - x^2}$.
b) The domain
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