Label the upper right hand corner of the
rectangle (x,y):



Now if we just look at the right half of that
rectangle, we have:



The area of the right half of the rectangle
is .

Therefore the area of the entire rectangle:



is twice that or 

.

However, that is the area in terms of both
x and y.  

We must get the area A in terms of just x.

So we replace  in  by 



Your teacher may want you to write  instead of 

If so the answer in functional notation is: 



Edwin