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# Maths problem watch

1. 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!
2. (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!
3. (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.
4. (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?
5. (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)
6. (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 . You agree?

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

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

We are given . You agree?

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

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

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

Thank you all
8. (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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