Hello, shirleychen888!
Did you make a sketch?
A rectangle is created with two left hand vertices on the yaxis.
One of the other vertices is on the line
. . and the other is on the line
Assuming the rectangle is bounded by the lines and the yaxis:
1) Write a formula for the area of the rectangle Code:
 y = 10x
10 * *
 * *
 * *
+* *
::::: *
:::::* *
+* *
 * *
  +  *      *   
 * 10 *
 * *
* y = 2x5
5 *

The area of a rectangle is: .
Our rectangle has: .
and: .
Therefore: .
2) What is the domain of ? Domain: .
3) Find the area when
4) Find the maximum area of the rectangle The graph of: is a downopening parabola.
. . Its maximum is at its vertex.
The vertex is at: .
The maximum area is: .