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    8) a cuboid has a square base of length x metres and heigh y metres
    a) express the volume V of the cuboid in terms of x and y
    b) show that the surface area of the cuboid is 2x^2 + 4xy
    - the surface area of the cuboid is 24cm ^2 -
    c) show that v = 6x - 0.5x^3
    d) show that the maximum volume of the box occurs when x = 2 and find this maximum volume

    ---Moved to maths---
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    (Original post by imaan2121)
    8) a cuboid has a square base of length x metres and heigh y metres
    a) express the volume V of the cuboid in terms of x and y
    b) show that the surface area of the cuboid is 2x^2 + 4xy
    - the surface area of the cuboid is 24cm ^2 -
    c) show that v = 6x - 0.5x^3
    d) show that the maximum volume of the box occurs when x = 2 and find this maximum volume

    ---Moved to maths---
    Sketch the cuboid, so you have something to reference back to during your workings.

    a) Do you know the formula for the volume of a cuboid?

    b) Do you know the formula for the surface area of a cuboid?

    What part are you stuck on exactly?
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    (Original post by Naruke)
    Sketch the cuboid, so you have something to reference back to during your workings.

    a) Do you know the formula for the volume of a cuboid?

    b) Do you know the formula for the surface area of a cuboid?

    What part are you stuck on exactly?
    I got the volume as x^2y, but don't know how the surface are = 2x^2 + 4y
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    (Original post by imaan2121)
    I got the volume as x^2y, but don't know how the surface are = 2x^2 + 4y
    Imagine this cuboid with two square faces that have length and width x and x and four other faces with length and width x and y. The area of the faces that are square is equal to the length multiplied by the width so it will be x*x, which is x^2. As there are two squares faces you multiply this by two to get 2x^2.

    Afterwards, you obtain the area of the other faces by multiplying x by y, getting xy. As there are four faces, you multiply this by 4 to get 4xy.

    As this is total surface area, you must add all of the surface areas together, which adds up to 2x^2 + 4xy
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    (Original post by imaan2121)
    8) a cuboid has a square base of length x metres and heigh y metres
    a) express the volume V of the cuboid in terms of x and y
    b) show that the surface area of the cuboid is 2x^2 + 4xy
    - the surface area of the cuboid is 24cm ^2 -
    c) show that v = 6x - 0.5x^3
    d) show that the maximum volume of the box occurs when x = 2 and find this maximum volume

    ---Moved to maths---
    Rewrite yor answer to a and sub into the result for b to get c.
    Differentiate and set to 0 to find d.
 
 
 
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