Let x and y be the length and area of the rectangle, respectively.
The arrow at the end of the line implies that it keeps growing indefinitely; therefore the range of the function is
[tex]\text{range}=\mleft\lbrace y\in\R|y\ge0\mright\rbrace=y\ge0[/tex]
Where we considered that the minimum of the function is at (0,0).
Similarly, the minimum value that x can take is zero because it is a length; then, the domain of the function is
[tex]\text{domain}=\mleft\lbrace x\in\R|x\ge0\mright\rbrace=x\ge0[/tex]
The range is y>=0 and the domain is x>=0
