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# Maximum and minimum problem watch

1. Hello everyone.

I need some guidence on how to do part a for this question. Can you help?
2. The quality is terrible post a better pic man
3. If you could rotate the image that would be helpful
4. Attachment 475615
Hope that this one is better quality, and it is the right way round. :-)
5. (Original post by Electrogeek)
Hope that this one is better quality, and it is the right way round. :-)
ya first post was upside-down, and the second is an invalid attachment...

Upload it to http://imgur.com/ and then wrap it in [img] tags to guarantee it'll work
6. http://imgur.com/6ewpWW2

Here's a link to the photo with the problem. I only need help with part a. :-)
7. (Original post by Electrogeek)

Hello everyone.

I need some guidence on how to do part a for this question. Can you help?
Well, what does the fact that she used 72 square metres of wood say about the surface area of the bookcase? Once you've written that down, use those dimensions to find an expression for V, and then use both pieces of information to eliminate d and get the required result
8. (Original post by Indeterminate)
Well, what does the fact that she used 72 square metres of wood say about the surface area of the bookcase? Now use those dimensions to find an expression for V, and that will enable you to eliminate d and get the required result
So do you mean that x times d times x/2 will give it, or do I have to use the net to make 72?
9. (Original post by Electrogeek)
So do you mean that x times d times x/2 will give it, or do I have to use the net to make 72?
You have to write down 2 things, the first of which you already know about (the volume).

The second thing to write down is the surface area, which you know is 72.

Both of these things involve d, but you can use the information about the surface area in order to make d the subject and get V in terms of x only
10. (Original post by Indeterminate)
You have to write down 2 things, the first of which you already know about (the volume).

The second thing to write down is the surface area, which you know is 72.

Both of these things involve d, but you can use the information about the surface area in order to make d the subject and get V in terms of x only
So d= -x/6 + 24/x? (this is for the surface area)
11. (Original post by Electrogeek)
So d= -x/6 + 24/x? (this is for the surface area)
Yep, now substitute that into the expression for V and you're done
12. (Original post by Indeterminate)
Yep, now substitute that into the expression for V and you're done
Thanks. :-)

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