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    Hi

    This is the data from a French exercise book:

    take a rectangle with perimeter 40cm

    one side = x
    calculate the other side (y) in term of x knowing that the area is x(20-x)



    I worked out that xy=x(20-x) and 2x + 2y =40

    if xy=x(20-x) ; y= x(20-x)/x = 20 -x

    so, substituting

    2x +2y =40 ; 2x(20-x) =40

    2x + 40 + - 2x =40

    and 40=40 !!

    The quations suggests, asks to show that the area is x(20-x)

    I am at a loss!

    help!
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    (Original post by Jorge)
    Hi

    This is the data from a French exercise book:

    take a rectangle with perimeter 40cm

    one side = x
    calculate the other side (y) in term of x knowing that the area is x(20-x)



    I worked out that xy=x(20-x) and 2x + 2y =40

    if xy=x(20-x) ; y= x(20-x)/x = 20 -x

    so, substituting

    2x +2y =40 ; 2x(20-x) =40

    2x + 40 + - 2x =40

    and 40=40 !!

    The quations suggests, asks to show that the area is x(20-x)

    I am at a loss!

    help!
    Would you mind giving us the actual question in the book, perhaps a picture of it? That would help immensely!
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    (Original post by Jorge)
    Hi

    This is the data from a French exercise book:

    take a rectangle with perimeter 40cm

    one side = x
    calculate the other side (y) in term of x knowing that the area is x(20-x)



    I worked out that xy=x(20-x) and 2x + 2y =40

    if xy=x(20-x) ; y= x(20-x)/x = 20 -x

    so, substituting

    2x +2y =40 ; 2x(20-x) =40

    2x + 40 + - 2x =40

    and 40=40 !!

    The quations suggests, asks to show that the area is x(20-x)

    I am at a loss!

    help!
    You have done the question; "find y in terms of x".

    y = 20 - x

    This is y in terms of x.
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    (Original post by Jorge)
    help!
    You start by saying "knowing the area is x(20-x)" and finish with "asks to show that the area is x(20-x)". That doesn't make sense.

    Do you have a link to the original question or photo/scan?
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    (Original post by ghostwalker)
    You start by saying "knowing the area is x(20-x)" and finish with "asks to show that the area is x(20-x)". That doesn't make sense.

    Do you have a link to the original question or photo/scan?
    The only data is:
    perimeter of a rectangle ABCD :40cm


    Question:

    Calculate BC (one side of the rectangle) in terms of x, and demonstrate that the area of the rectangle is x(20-x)
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    (Original post by Jorge)
    The only data is:
    perimeter of a rectangle ABCD :40cm


    Question:

    Calculate BC (one side of the rectangle) in terms of x, and demonstrate that the area of the rectangle is x(20-x)
    You've pretty much already done what the question asked you to

    We are given \displaystyle 2x + 2y = 40 \iff x+y = 20. You agree?

    So let us find the side y in terms of x: y = 20 -x. You have now found BC in terms of x. Ta-da

    You now have two sides of a rectangle, one is x and the other is 20-x, what is the area now?
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    (Original post by Zacken)
    You've pretty much already done what the question asked you to

    We are given \displaystyle 2x + 2y = 40 \iff x+y = 20. You agree?

    So let us find the side y in terms of x: y = 20 -x. You have now found BC in terms of x. Ta-da

    You now have two sides of a rectangle, one is x and the other is 20-x, what is the area now?

    Yes, that makes sense. It's so simple that it became complicated....

    Thank you all
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    (Original post by Jorge)
    Yes, that makes sense. It's so simple that it became complicated....

    Thank you all
    Glad you got it!
 
 
 
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