You are not logged in.
#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.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#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.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#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.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#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.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.