rectangular plot of farm land will be bounded on one side by a river and the other 3 sides by a single strand of electric wire. With 800 metres of wire at your disposal what is the largest area you can enclose and what are its dimensions.

my answers : 80000m^2

1st I let the perimeter = 800

2y+x= 800

then i subbed into the equation for the area A=xy and let it equal to zero.

but i got to differentiate is this wrong?

could someone verify my anwer?