Question 764039
One side would be 300-x and the other side side lengths are each x.  The area in general is a function of x.
{{{A(x)=x(300-x)}}} and the length of fencing is 300.


We can use the function in factored form to find the zeros.  The x value in exactly the middle of the zeros is that at which A is either a minimum or a maximum.  Here, we can see that A(x) is {{{-x^2+300}}}, which is a parabola with a maximum, seeing that the coefficient on x^2 term is {{{-1}}}.  


With that, can you find the maximum area?  
(BIG HINT: A=0 when x=0 or x=300)