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Section 4.9 : More Optimization

  1. We want to construct a window whose middle is a rectangle and the top and bottom of the window are semi-circles. If we have 50 meters of framing material what are the dimensions of the window that will let in the most light?
    A sketch of the window described in the problem.  It is a rectangle with a semicircle on the top and another semicircle on the bottom, and dashed lines mark where the top and bottom of the rectangle meet the flat sides of the two semicircles.
    Solution
  2. Determine the area of the largest rectangle that can be inscribed in a circle of radius 1.
    A sketch of a rectangle inscribed in a circle.  All four corners of the rectangle touch the circle and the rectangle is wider than it is tall.
    Solution
  3. Find the point(s) on \(x = 3 - 2{y^2}\) that are closest to \(\left( { - 4,0} \right)\). Solution
  4. An 80 cm piece of wire is cut into two pieces. One piece is bent into an equilateral triangle and the other will be bent into a rectangle with one side 4 times the length of the other side. Determine where, if anywhere, the wire should be cut to maximize the area enclosed by the two figures. Solution
  5. A line through the point \(\left( {2,5} \right)\) forms a right triangle with the \(x\)-axis and \(y\)-axis in the 1st quadrant. Determine the equation of the line that will minimize the area of this triangle.
    A sketch of the triangle described in the problem.  A line falls from the upper left to the lower right, passing through the point \(\left( {2,5} \right)\), which is marked on the line.  The line together with the x-axis and the y-axis forms a right triangle in the first quadrant and the inside of the triangle is shaded and labeled “Minimize This Area”.
    Solution
  6. A piece of pipe is being carried down a hallway that is 18 feet wide. At the end of the hallway there is a right-angled turn and the hallway narrows down to 12 feet wide. What is the longest pipe (always keeping it horizontal) that can be carried around the turn in the hallway?
    A sketch of the hallway described in the problem, seen from above.  The wide hallway is 18 feet across and runs vertically, the narrow hallway is 12 feet across and runs horizontally, and they meet at a right-angled turn.  The pipe is drawn as a straight line lying diagonally across the inside corner of the turn, touching the outer wall of each hallway and resting against the inner corner.
    Solution
  7. Two 10 meter tall poles are 30 meters apart. A length of wire is attached to the top of each pole and it is staked to the ground somewhere between the two poles. Where should the wire be staked so that the minimum amount of wire is used?
    A sketch of the two poles and the wire.  Both poles are 10 meters tall and the ground between them is marked as 30 meters.  The wire runs from the top of the left pole down to a stake on the ground between the poles and then back up to the top of the right pole, forming a “V” shape.
    Solution