Brian asked in 科學及數學數學 · 1 decade ago

Please help!! Maths for 10 points

Please help me on this question:

A piece of wire of length 8 cm is cut into two pieces and each piece is bent into a sqaure. if the total area enclosed is minimum, find the length of the sides of each square

Please give me a detailed solution as I don't know how to do it

3 Answers

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  • 1 decade ago
    Favorite Answer

    The answer is 1cm

    The total area enclosed is minimum when the 2 wires are of equal length, i.e. 4cm and 4cm.

    Length of each side of square = 4cm divided by 4 = 1cm

    Total area = 1cm x 1cm + 1cm x 1cm = 2cm2

    If the wire is cut into 5cm and 3cm,

    - Length of each side of square is 5cm divided by 4 = 1.25cm and 3cm divided by 4 = 0.75cm

    - Total area is 1.25cm x 1.25cm + 0.75cm x 0.75cm = 2.125cm2

    If the wire is cut into 6cm and 2 cm,

    Length of each side of square is 6cm divided by 4 = 1.5cm and 2cm divided by 4 = 0.5cn

    Total area is 2.25cm2 + 0.25cm2 = 2.5cm

    If the wire is cut into 7cm and 1 cm

    Length of each side of square is 7cm divided by 4 = 1.75cm and 1 cm divided by 4 = 0.25cm

    Total area is 3.0625cm2 + 0.0625cm2 = 3.125cm2

    Therefore, total area enclosed is minimum when the wire is cut into two equal pieces (4cm and 4cm). The length of the side of each square is therefore 1cm.

  • ?
    Lv 7
    1 decade ago

    Let X be the lenght of one of the piece of wire.

    Then 8-X be the lenght of the other piece of wire.

    Side of the squares: X/4 and (8-X)/4

    Area of the squares

    = X/4 * X/4 + (8-X)/4 * (8-X)/4

    = (X^2 + 64 - 16X + X^2) / 16

    = (2X^2 -16X + 64) / 16

    To find the minimum, take derivative with respect to X, and set it to zero

    d Area / d X = (4X - 16) / 16 = 0

    X = 4

    Therefore, the wire is cut into two pieces with the same lenght 4cm.

    Side of the two squares = 4cm / 4 = 1cm

  • 1 decade ago

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    含數學史、教學資源、活動及相關網址等資訊。

    www.edp.ust.hk/math -

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