# How do u "set" x = 0 ???

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Is there a way to describe how you set x=0 "in the classical phyiscal sense" or before QM came along??

I'm just looking for a straight forward simple answer.

Example:

Say we have 4 points ascending on a curve in the up direction in Cartessian Space.

1 2 3 4 and we want to measure a change between 3 and 4

Do we say x= 3 =0 and x= 4 = 1

???

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In the equation
Y=3x2+25

setting  x=0  means considering what happens to that function when x=0

You get

y=3(0)2+25
y=0+25
y=25

IOW, the function crosses the Y axis at 25 when x=0 ( origin of x axis )

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5 hours ago, MigL said:

In the equation
Y=3x2+25

setting  x=0  means considering what happens to that function when x=0

You get

y=3(0)2+25
y=0+25
y=25

IOW, the function crosses the Y axis at 25 when x=0 ( origin of x axis )

Understood, but I think I forgot to mention setting x->0 for limits, changes in dx/dy

Such as, Lim x->0

x^2-25/x-5

Plugging 5 into x

In this case does 0 still refference (origin of x axis)?

Not sure my example makes the point becuase their are many ways to express the same "concept."

Correct me if I'm wrong..

Becuase the origin is space itself "cartessian space that is" x axis..

Edited by CuriosOne
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Taking lim x->0 is not the same as setting x = 0

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Quote

Understood, but I think I forgot to mention setting x->0 for limits, changes in dx/dy

Such as, Lim x->0

x^2-25/x-5

Plugging 5 into x[/quote]

No, you do not find the limit by "plugging 5 into x".  You should see that "plugging 5 into x" gives 0/0 which is NOT a number.

There is a theorem that says "if for some  interval  containing x= a, f(x)= g(x) for all x except possibly x= a then $$\lim_{x\to a} f(x)= \lim_{x\to a} g(x)$$".

Here $$\frac{x^2- 25}{x- 5}= \frac{(x+ 5)(x- 5)}{x- 5}= x+ 5[/TEX] for all x EXCEPT x= 5, [tex]\lim_{x\to 5}\frac{x^2- 25}{x-5}= \lim_{x\to 5} x+ 5$$ and that is 5+ 5= 10 because x+ 5 is CONTINUOUS.

In this case does 0 still refference (origin of x axis)?

0 "references" the number zero.

Not sure my example makes the point becuase their are many ways to express the same "concept."

Correct me if I'm wrong.."

Edited by HallsofIvy
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8 hours ago, swansont said:

Taking lim x->0 is not the same as setting x = 0

Im totally confused...

Is this becuase taking a limit uses 2 points on the cartessian cooridinent system??

7 hours ago, HallsofIvy said:

Great explanation, but in this case and is in all cases dealing with limits its not exactly 25 its x = 24.999...

So what happens then??

Does this explain the difference between setting x=0 and taking a limit as x->0 ??

I think this is very important stuff...

Edited by CuriosOne
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Frankly it appears that you do not know what "limits" are!   If you did, you would know that "24.999....." IS exactly  25.

Taking a limit does NOT "involve two points", it involves infinitely many points.  Taking "the limit as x goes to a"  involves all the points between $$a- \delta$$ and $$a+ \delta$$ and, no matter how small $$\delta$$ is, there are infinitely many points between those points.

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8 hours ago, CuriosOne said:

Im totally confused...

Is this becuase taking a limit uses 2 points on the cartessian cooridinent system??

Limits involve the behavior of a function that might diverge (e.g. it can depend on the value and the slope of the function). Setting a variable equal to a value only involves evaluating the function at one point. You wouldn’t bother with a limit if you could just do the arithmetic of evaluating the function. e.g. you don’t need to look at a limit for x^2 for any finite value of x.

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10 hours ago, HallsofIvy said:

Frankly it appears that you do not know what "limits" are!   If you did, you would know that "24.999....." IS exactly  25.

Taking a limit does NOT "involve two points", it involves infinitely many points.  Taking "the limit as x goes to a"  involves all the points between $$a- \delta$$ and $$a+ \delta$$ and, no matter how small $$\delta$$ is, there are infinitely many points between those points.

No, i meant 2 things, ""a derivitive"" ""needs 2 points"" and I meant that if a limit is 5, then approaching it "getting close to it" can only be a maximum value of 4.99999, i gave the backwards example...Here is a table..

Also, there needs to be a "span" inbetween say 0.001 for a total of 5,000 points "only" not an infinite amount that's crazy.

24.999 is "not the same" as 25

10 hours ago, swansont said:

Limits involve the behavior of a function that might diverge (e.g. it can depend on the value and the slope of the function). Setting a variable equal to a value only involves evaluating the function at one point. You wouldn’t bother with a limit if you could just do the arithmetic of evaluating the function. e.g. you don’t need to look at a limit for x^2 for any finite value of x.

I thought "all limits" involved 4 points..

Maybe Derivitves, Difference Quotient or delta h can get my point across here..

F(x) = F(x-dx)^2 - F(x)^2/ delta h

Becuase y2-y1/x2-x1 is linear is 4 points..

I also just wanted to note:

To say x is to imply it has a base of +1

ie x^1 it's simple things like this that cause "much" confusion..

Edited by CuriosOne
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44 minutes ago, CuriosOne said:

I also just wanted to note:

To say x is to imply it has a base of +1

I have no idea what this is supposed to mean

Quote

24.999 is "not the same" as 25

24.999 is not the same as 24.999...

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24 minutes ago, swansont said:

I have no idea what this is supposed to mean

24.999 is not the same as 24.999...

Basically the root of 24.999999999

with 8 "nines"

Is 4.999999999

With 9 "nines"

As far as my T1-84 Plus CE

A root is x^1/2 as 25^1/2 = 5

As with 24.999 and 25

And as with 24^1/1+2 = the root of 8

The 9 and 8 "Are To, Not The Same Number"

Unless of coarse +24.99 and -24.99 cancell to 0...Then were back to square one, the x^1 thing going on here.

Edited by CuriosOne
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10 hours ago, CuriosOne said:

Basically the root of 24.999999999

with 8 "nines"

Is 4.999999999

With 9 "nines"

As far as my T1-84 Plus CE

A root is x^1/2 as 25^1/2 = 5

As with 24.999 and 25

And as with 24^1/1+2 = the root of 8

The 9 and 8 "Are To, Not The Same Number"

Unless of coarse +24.99 and -24.99 cancell to 0...Then were back to square one, the x^1 thing going on here.

None of the numbers you mentioned are 24.999... so why do you think this is relevant? Do you understand what is meant by the ellipses at the end of the number?

And I can’t even tell if you attempted to explain what you meant by “To say x is to imply it has a base of +1”

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1 hour ago, swansont said:

And I can’t even tell if you attempted to explain what you meant by “To say x is to imply it has a base of +1”

He certainly didn't make a successful attempt.

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3 hours ago, John Cuthber said:

He certainly didn't make a successful attempt.

Neither has anyone else in the "history" of science, some refer to it as the conservation of energy, the positive of its anti, yin and yang, good and evil, """Alice and Bob"""" male and female, 0 binary 1 binary, black or white, day and nite etc etc..

5 hours ago, swansont said:

None of the numbers you mentioned are 24.999... so why do you think this is relevant? Do you understand what is meant by the ellipses at the end of the number?

And I can’t even tell if you attempted to explain what you meant by “To say x is to imply it has a base of +1”

3.45...<----- The three dots imply the numbers go on forever, some numbers can repeat or never terminate..

""But I have no idea if that's true.""

I hope we understand I'm talking about 2 points....Y2-Y1/X1-X2.

Distance, where order of operations does not matter..

But as the ""difference quotient""of instantaneous change, differntiation dirivitives.

""""""This is what the OP is asking"""""

The x->0 is saying the variable x is already a "fraction" of y, from some other whole number or "region" "time domain" within the function f(x) itself..

I assume that's why scientist bother with this concept in the first place...

To say 1/4 = 0.25 would mean 1 =100

Why not just say 100/4

This is why x^1 of x^2 or f of (f)x  is "obviously saying" and I think we all know this 1 = 100 the centi meter unit 10^-2

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34 minutes ago, CuriosOne said:

To say 1/4 = 0.25 would mean 1 =100

Not even remotely close.  You're a lost ball in high weeds, when it comes to math.

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1 hour ago, CuriosOne said:

3.45...<----- The three dots imply the numbers go on forever, some numbers can repeat or never terminate..

Correct!

So how come in all of your responses to this issue you never use or acknowledges this?

1 hour ago, CuriosOne said:

""But I have no idea if that's true.""

I hope we understand I'm talking about 2 points....Y2-Y1/X1-X2.

Distance, where order of operations does not matter..

But as the ""difference quotient""of instantaneous change, differntiation dirivitives.

""""""This is what the OP is asking"""""

The OP asks how you set x=0.

Y2-Y1/X1-X2 is different

1 hour ago, CuriosOne said:

The x->0 is saying the variable x is already a "fraction" of y, from some other whole number or "region" "time domain" within the function f(x) itself..

There is no limit involved in evaluating Y2-Y1/X1-X2

1 hour ago, CuriosOne said:

To say 1/4 = 0.25 would mean 1 =100

No, that’s not what it means

1 hour ago, CuriosOne said:

Why not just say 100/4

Because 1 ≠ 100 and 0.25 ≠ 25

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The following is an easy to understand overview of derivatives.

Come back and ask questions when you're done ...

Don't seem to be able to attach this file ??

Haven't done this for a long time. Can anyone offer advice ?

Edited by MigL
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3 hours ago, Bufofrog said:

Not even remotely close.  You're a lost ball in high weeds, when it comes to math.

-0.1÷24-5= -5.0041^2 * 4  = 100.16...

Make sure to use the entire -0.1÷24-5 in your calculator otherwise you get.

-0.1/19=-0.005263^2 *4 =1.1e-4

Yea, i'm pretty lost alright..🤣🤣🤣

2 hours ago, MigL said:

The following is an easy to understand overview of derivatives.

Come back and ask questions when you're done ...

Don't seem to be able to attach this file ??

Haven't done this for a long time. Can anyone offer advice ?

I will spend hours studying this...Thnx..

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4 hours ago, CuriosOne said:

Neither has anyone else in the "history" of science, some refer to it as the conservation of energy, the positive of its anti, yin and yang, good and evil, """Alice and Bob"""" male and female, 0 binary 1 binary, black or white, day and nite etc etc..

Nobody else has explained  this

21 hours ago, CuriosOne said:

To say x is to imply it has a base of +1

because you just made it up.

Why not try to explain what you mean by it?

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47 minutes ago, John Cuthber said:

Nobody else has explained  this

because you just made it up.

Why not try to explain what you mean by it?

If I explained it, it would diverge the OP and be considered off topic...

I just wanted to make note of it becuase people tend to forget including myself all the time..

y = x^2 or 2x "algeabraically" forgets to tell us, "By the way when you see x its implied that x has a base of 1..x^1

The base could be 10,  2, 3, 12 etc

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26 minutes ago, CuriosOne said:

If I explained it, it would diverge the OP and be considered off topic...

I just wanted to make note of it becuase people tend to forget including myself all the time..

y = x^2 or 2x "algeabraically" forgets to tell us, "By the way when you see x its implied that x has a base of 1..x^1

The base could be 10,  2, 3, 12 etc

Maybe you should stick to asking questions, and refrain from passing along such “insights”

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6 minutes ago, swansont said:

Maybe you should stick to asking questions, and refrain from passing along such “insights”

Physics is about "observation' location and prediction...Math is just a "tool."

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2 hours ago, CuriosOne said:

I will spend hours studying this...Thnx..

Mine says I do not have permission to open ( my own file ).

Anyway study it it well and if anything confuses, ask questions about it.

9 minutes ago, CuriosOne said:

Math is just a "tool."

Better learn how to use that tool.

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1 hour ago, MigL said:

Mine says I do not have permission to open ( my own file ).

Anyway study it it well and if anything confuses, ask questions about it.

Better learn how to use that tool.

Oh yes I will, trust me..Your PDF is already doing that, thnks again..

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• 2 weeks later...

Now I'm hoping that all of your posts are silly jokes.  Otherwise, you not only do not know but are refusing to learn from those that do know.  And you have asserted repeatedly that "no one knows"!

I think I am through responding to any of your posts.  It does no good,

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