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#1 2012-11-11 09:09:22
- John92
- Guest
Stuck trying to prove/show something
Hey guys, i'm doing an econ assignment but i'm either going about the question in completely the wrong way - or im stuck on some math that i'm unable to do. Assuming it's the second (because i dont just want to post the question and get you to do the whole thing for me), here's what im stuck on.
A = 9xy
B = 9x + 9y - 18xy
C = 9 - 9x - 9y + 9xy
D = 12xy - 6x - 6y + 6
I want to prove that there are no values of x and y (where x and y are both values between 0 and 1) for which D is the greatest.
Is that possible to do numerically? Only thing i can think of is having some software plot a 3d graph and show that the D surface is always below at least one other - obviously thats no good for helping me do my homework though lol.
#2 2012-11-11 09:16:16
- bobbym
- Administrator
Online
Re: Stuck trying to prove/show something
Hi;
D surface is always below at least one other
I am not following you here. Please post the exact question. Wording is very important in mathematics.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#3 2012-11-11 09:21:42
- John92
- Guest
Re: Stuck trying to prove/show something
Sorry, maybe ignore that bit, i'm not sure that even makes sense anyway - i was just speculating about how i'd demonstrate that at least one of the values, A, B, C would be greater than D at every value of x and y.
#4 2012-11-11 09:39:30
- bobbym
- Administrator
Online
Re: Stuck trying to prove/show something
If x,y were in the interval of 0 and 1?
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#6 2012-11-11 09:53:56
- bobbym
- Administrator
Online
Re: Stuck trying to prove/show something
Hi;
A is out, it is not always greater than D in the closed interval (0,1).
B is out, it is not always greater than D in the closed interval (0,1).
C is out, it is not always greater than D in the closed interval (0,1).
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#7 2012-11-11 10:04:55
- anonimnystefy
- Real Member
Offline
Re: Stuck trying to prove/show something
I don't think the point is to prove that one of those is always greater than D, but rather at least one of those will be greater than D for some x and y.
The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón
#8 2012-11-11 10:49:13
- bobbym
- Administrator
Online
Re: Stuck trying to prove/show something
Hi;
that at least one of the values, A, B, C would be greater than D at every value of x and y
Looks like he is saying A or B or C is always greater in that interval.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.