Precalculus (6th Edition) Blitzer

$P(x)=\dfrac{2x^2+2000}{x}$
Consider $x$ and $y$ to be the width and height. Thus, $Area = width \times height=xy$ so, $y= \dfrac{1000}{x}$ This implies that $P(x)=2x+\dfrac{2000}{x}=\dfrac{2x^2+2000}{x}$ Therefore, $P(x)=\dfrac{2x^2+2000}{x}$