Section 5.5: Applied Maximum and Minimum Problems
Example: A farmer wants to fence an area of 24 million square feet in a rectangular field and
then divide it in half with a fence parallel to one of the sides of the rectangle. What should
the lengths of the sides of the rectangular field be so as to minimize the cost of the fence?
Example: If 1200 cm2 of material is available to make a box with a square base and an open
top, find the largest possible volume of the box.
1
Example: A box with a square base and open top must have a volume of 4,000 cm3 . Find
the dimensions of the box that minimize the amount of material used.
Example: Find the point on the line 6x + 3y + 9 = 0 that is closest to the point (−1, −2).
2
Example: Find the dimensions of the rectangle of largest area that has its base on the x-axis
and its other two vertices above the x-axis and lying on the parabola y = 8 − x2 .
Example: Find the area of the largest rectangle that can be inscribed in a right triangle with
legs of lengths 3 cm and 4 cm if two sides of the rectangle lie along the legs.
3
Example: A poster is to have an area of 180 in2 with 1-inch margins at the bottom and sides
and a 2-inch margin at the top. What dimensions will give the largest printed area?
Example: A cylindrical can is made to contain V cm3 of liquid. Find the dimensions that
will minimize the cost of the metal to make the can.
4
Example: A piece of wire 10 m long is cut into two pieces. One piece is bent into a square
and the other into a circle. How should the wire be cut so that the total area enclosed is a
maximum?
5