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Section 4.9 : More Optimization

  1. We want to construct a window whose bottom is a rectangle and the top of the window is an equilateral triangle. If we have 75 inches of framing material what are the dimensions of the window that will let in the most light?
  2. We want to construct a window whose middle is a rectangle and the top and bottom of the window are equilateral triangles. If we have 4 feet of framing material what are the dimensions of the window that will let in the most light?
  3. We want to construct a window whose middle is a rectangle, the top of the window is a semicircle and the bottom of the window is an equilateral triangle. If we have 1500 cm of framing material what are the dimensions of the window that will let in the most light?
  4. Determine the area of the largest rectangle that can be inscribed in a circle of radius 5.
    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.
  5. Determine the area of the largest rectangle whose base is on the \(x\)-axis and the top two corners lie on semicircle of radius 16.
    A sketch of a semicircle sitting on the x-axis with a rectangle inscribed in it.  The base of the rectangle lies along the x-axis and the top two corners of the rectangle touch the semicircle.
  6. Determine the area of the largest rectangle whose base is on the \(x\)-axis and the top two corners lie \(y = 4 - {x^2}\).
    A sketch of the downward opening parabola \(y = 4 - {x^2}\) with a rectangle inscribed under it.  The base of the rectangle lies along the x-axis and the top two corners of the rectangle touch the parabola.
  7. Find the point(s) on \(\displaystyle \frac{{{x^2}}}{4} + \frac{{{y^2}}}{{36}} = 1\) that are closest to \(\left( {0,1} \right)\).
  8. Find the point(s) on \(x = {y^2} - 8\) that are closest to \(\left( {5,0} \right)\).
  9. Find the point(s) on \(y = 2 - {x^2}\) that are closest to \(\left( {0, - 3} \right)\).
  10. A 6 ft 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 twice the length of the other side. Determine where, if anywhere, the wire should be cut to minimize the area enclosed by the two figures.
  11. A 250 cm piece of wire is cut into two pieces. One piece is bent into an equilateral triangle and the other will be bent into circle. Determine where, if anywhere, the wire should be cut to maximize the area enclosed by the two figures.
  12. A 250 cm piece of wire is cut into two pieces. One piece is bent into an equilateral triangle and the other will be bent into circle. Determine where, if anywhere, the wire should be cut to minimize the area enclosed by the two figures.
  13. A 4 m piece of wire is cut into two pieces. One piece is bent into a circle and the other will be bent into a rectangle with one side three 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.
  14. A line through the point \(\left( { - 4,1} \right)\) forms a right triangle with the \(x\)-axis and \(y\)-axis in the 2nd 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 rises from the lower left to the upper right, passing through the point \(\left( { - 4,1} \right)\), which is marked on the line.  The line together with the x-axis and the y-axis forms a right triangle in the second quadrant and the inside of the triangle is shaded and labeled “Minimize This Area”.
  15. A line through the point \(\left( {3,3} \right)\) 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 \(\left( {3,3} \right)\), 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”.
  16. A piece of pipe is being carried down a hallway that is 14 feet wide. At the end of the hallway there is a right-angled turn and the hallway narrows down to 6 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 14 feet across and runs vertically, the narrow hallway is 6 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.
  17. A piece of pipe is being carried down a hallway that is 9 feet wide. At the end of the hallway there is a right-angled turn and the hallway widens up to 25 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 first hallway is 9 feet across and runs vertically, the second hallway is 25 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.
  18. Two poles, one 15 meters tall and one 10 meters tall, are 40 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.  The 15 meter pole is on the left, the 10 meter pole is on the right and the ground between them is marked as 40 meters.  The wire runs from the top of the taller pole down to a stake on the ground between the poles and then back up to the top of the shorter pole, forming a “V” shape.
  19. Two poles, one 2 feet tall and one 5 feet tall, are 3 feet 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.  The 2 foot pole is on the left, the 5 foot pole is on the right and the ground between them is marked as 3 feet.  The wire runs from the top of the shorter pole down to a stake on the ground between the poles and then back up to the top of the taller pole, forming a “V” shape.
  20. Two poles, one 15 meters tall and one 10 meters tall, are 40 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 angle formed by the two pieces of wire at the stake is a maximum?
    A sketch of the two poles and the wire.  The 15 meter pole is on the left, the 10 meter pole is on the right and the ground between them is marked as 40 meters.  The wire runs from the top of the taller pole down to a stake on the ground and then back up to the top of the shorter pole, and the angle formed by the two pieces of wire at the stake is labeled \(\theta \).
  21. Two poles, one 34 inches tall and one 17 inches tall, are 3 feet 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 angle formed by the two pieces of wire at the stake is a maximum?
    A sketch of the two poles and the wire.  The 34 inch pole is on the left, the 17 inch pole is on the right and the ground between them is marked as 3 feet.  The wire runs from the top of the taller pole down to a stake on the ground and then back up to the top of the shorter pole, and the angle formed by the two pieces of wire at the stake is labeled \(\theta \).
  22. A trough for holding water is to be formed as shown in the figure below. Determine the angle \(\theta \) that will maximize the amount of water that the trough can hold.
    The base of the trough is shown and labeled “30 in”.  There is also a lighter gray shaded line that extends out from the right and left side of the base of the trough.  The two sides are shown and also labeled “30 in”.  The angle that each side makes with the gray line underneath is given as $\theta$.
  23. A trough for holding water is to be formed as shown in the figure below. Determine the angle \(\theta \) that will maximize the amount of water that the trough can hold.
    The base of the trough is shown and labeled “4 m”.  There is also a lighter gray shaded line that extends out from the right and left side of the base of the trough.  The two sides are shown and labeled “1 m”.  The angle that each side makes with the gray line underneath is given as $\theta$.