incredible something happen to me in math related to logic

Ryan$

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Jan 25, 2019
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To be more frankly here, I know my skills and I'm not that good much at math and LOGIC , Everyday I struggle to be better and I read more and more, but I really need your help guys and about one week something happen to me related to logic to solve the problem.
my problem is like this: I have a problem, I solve it, I arrive for instance to conclusion like this:
(1) x=y
(2)x+z=f
so once I arrive to the second equation which is x+z=f, in my head I know that's x=y, but what's confusing me is, is it legitimate to go to the first equation and afterwards going to the second equation for assigning ? I mean I know x=y, but who said that's legal to take myself to the first equation, grabbing data from their, and going with those data to the second equation and manipulate the grabbed data over the second equation?
once again, my problem isn't that I don't know that x=y or whatever, again and again, once I reach the second equation x+z=f, totally I know and still remember that x=y, but my confusion is, who said that it's legal to go to the first equation and grabbing from their the logic of the first equation, and manipulate that logic to the second equation?!!! here's totally my point!

Anyone can help me by an analogy to our real life that "manipulating LOGIC of first equation to the other equations is totally legitimate" and going, grabbing from equations and connect between them is "throughout true" and not mess the logic.

to clear more, who said it's legal to "go" from logic of first equation to manipulate it over other equations? is "going" something legal?

Sorry once again for that but I'm struggling that problem
 

Dr.Peterson

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Please quote the actual problem you are working on here, in its entirety. That will make all the difference. In particular, we need to see whether these are two parts of one problem, or two separate problems; and we need to see what the goal is that they are asking you to accomplish. That is what can tell you whether it is legitimate to use one in the other.

A problem you have made up or simplified from something larger is not sufficient. Until you do that, there is really nothing to say.
 

JeffM

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I agree with Dr. P that we need to see the specific problem to do anything concrete.

In general, however, your questions frequently seem to be about names. In the context of a given problem, whenever you assign a name to a specific concept, that name pertains to that specific mental concept throughout the problem. The x's, y's, etc. are names. If you say "Washington" means the capital of the US in a given problem, "Washington" does not come to mean the first president of the US within that problem.
 

HallsofIvy

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Frankly, I can't figure out what Ryan$ is trying to say! If x= y and x+ z= f then you can say that y+ z= f because "x" and "y" are just different ways of saying the same thing. Or, from x+ z= f, x= f- z so f- z= y.
 

Denis

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As I told you earlier Ryan, we can't tell what you're asking ...
 

Ryan$

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Please quote the actual problem you are working on here, in its entirety. That will make all the difference. In particular, we need to see whether these are two parts of one problem, or two separate problems; and we need to see what the goal is that they are asking you to accomplish. That is what can tell you whether it is legitimate to use one in the other.

A problem you have made up or simplified from something larger is not sufficient. Until you do that, there is really nothing to say.
My problem that if I have two equations, for instance:
(1) x=y
(2)x+f=z
once I arrive to the second equation, while I read the first equation, I know that x=y, but not assigning that although literally I know x=y from the first equation ! so what's that problem? am I have a mentally problem? I mean is it my mentally problem, or I need to practice to start think in another way?
once again I know that I must assign x=y when I read the second equation but my mind tells me to not assign ! how can I solve that problem?>!
 

Dr.Peterson

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Please do what you are asked. We want to see an actual problem you found somewhere, not one that you have made up that would never be given. I can't answer you until you cooperate.
 

JeffM

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Please do what you are asked. We want to see an actual problem you found somewhere, not one that you have made up that would never be given. I can't answer you until you cooperate.
I do not think that there is a real problem. I think Ryan thinks that he can understand generalizations without any reference to the specifics that the generalization represents. Without understanding the generalization, he tries to do so by making up problems purportedly involving the generalization. Needless to say, you cannot dispel ignorance through ignorance.

Ryan

\(\displaystyle x = y \text { and } x + f = z \implies y + f = z.\)

If that conclusion is helpful, you can use it.
 

HallsofIvy

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Do you understand what "=" means?
 
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