7.3.5 The Wire-Cutting Problem Flashcards Preview

AP Calculus AB > 7.3.5 The Wire-Cutting Problem > Flashcards

Flashcards in 7.3.5 The Wire-Cutting Problem Deck (5):
1

note

- Values that make the derivative of a function equal to 0 or undefined are candidates for maxima and minima of the function.
- The wire cutting problem involves minimizing the sum of the areas of a square and a circle formed from a fixed length of material.
- For a given perimeter, a circle encloses more area than a square does.

2

note

- In this problem you are asked to find where a wire
should be cut so that the area made by the resulting
two pieces is minimized.
- You know the length of the wire, the formulas for the
area and perimeter of the square, and the formulas
for the area and circumference of the circle.
- Since the perimeter plus the circumference equals
the total length of the wire, you can relate the area
to the length of the wire by expressing the perimeter
(or sides of the square) in terms of the
circumference. This will enable you to express the
area in terms of a single variable, namely c.
- Differentiate the area to find the minimum
candidate. Do not forget to check that the candidate
is indeed a minimum.
- Knowing the circumference tells you where to cut
the wire.
- Circles pack area more efficiently than squares. So
if you want to minimize the sum of the two areas, it
makes sense that you would want the square to be
bigger.

3

A 16 inch wire is cut in two and shaped into two squares. What is the minimum possible sum of the two areas?

Asum = 8 in^2

4

A 12 inch wire is being cut into two pieces which are then shaped into a circle and a regular octagon of maximum area. What is the sum of the perimeters?

12 inches

5

A 24 inch wire is cut in two and shaped into a square and a regular octagon. What is the minimum possible sum of the two areas?AOctagon=(2+2√2)s^2

Asum  = 19.689in^2

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