Why Use a Dummy Variable in the Fundamental Theorem of Calculus?

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SUMMARY

The discussion centers on the necessity of using a dummy variable, such as 't', in the Fundamental Theorem of Calculus (FTC), specifically in the expression \frac{d}{dx} \int^x_a f(t)dt= f(x). Participants emphasize that using 't' distinguishes the variable of integration from the limit of integration, 'x', preventing confusion and ensuring clarity in mathematical communication. The consensus is that using the same variable for both roles leads to ambiguity and undermines the integrity of the theorem.

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  • #61
cyrusabdollahi said:
What the bleep??...

i think it was in empire strikes back when obi-wan tells luke not to go try save leia/han/chewie/etc & that it's a trap, he should wait until his training is done before he faces darth vader, & yoda says "yes! to obi-wan you listen!"

edit: start at the beginning. can you tell us what is wrong (if anything) with writing
\sum_{n=0}^n f(n)
 
Last edited:
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  • #62
Sure, your index starts at n=0, and goes to n. That would be like going from 0 to 0. n only ever takes on one single value.
 
  • #63
how do you fix it & explain why it works the correct way
 
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  • #64
I love all of you! No, honestly, I am sorry for being a pain in your rear. I am thankful for all your help! (to mathwonk)
 
  • #65
Well, to make it work you would have to change the n on top of the sigma to some other value. Then n can increment from zero to, let's say r. ( if we change that n on top of sigma to r.)

\sum_{n=0}^r f(n) But I am not sure about the n inside the f(n), would it always remain at zero, or would it change? I think it would change. It would increment until it reaches the value of r and stops.
 
  • #66
the d3 thing. the thing is that what the person who first poted it was trying to get across was something silly. ok? no, if g is any function then the symbol dg(x) is the same as g'(x)dx. right? but the original use of this was not to refer to 3 as a constant function but to simply a number. it is moot what the intention was. I *can* give it meaning, but that isnt' necessarily what was intended. maths isn't abuot some set of things that exist and come with notation already.
 
  • #67
^^ stop confusing cyrus :cry:

cyrusabdollahi said:
Well, to make it work you would have to change the n on top of the sigma to some other value. Then n can increment from zero to, let's say r. ( if we change that n on top of sigma to r.)

\sum_{n=0}^r f(n) But I am not sure about the n inside the f(n), would it always remain at zero, or would it change? I think it would change. It would increment until it reaches the value of r and stops.

yeah, & it's similar with \int_{t=a}^{x} g(t)dt

just like you can give \sum_{n=0}^r f(n) a name like F(r), we can give \int_{t=0}^{x} g(t)dt a name like G(x), where G'(x) = g(x). the 'dummy variable' t 'increments' from 0 until it reaches the 'value' x.
 

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