Thread: max min problem

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?

Originally Posted by raoulduke1

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?

You need the area to only be a function of one variable.

From the first equation, you have , so substituting into the second gives



Now set the derivative equal to , solve, back-substitute, solve for .