My new U substitution approach? is this legal?

In summary, the speaker is proposing a new theory called the "Mancini conjecture" regarding integration by substitution. They suggest that if the exponent is positive, eventually taking the nth derivative will lead to a constant, making integration easier. However, it is mentioned that this approach may not work due to the need to add a constant when integrating. The speaker is unsure if their idea will work and suggests trying it out and checking the result by differentiating.
  • #1
mancini0
31
0
Allow me to explain my new theory, The "Mancini conjecture."

Ok...lets say I have an integral like (4-x^2)^(1/2) dx.

and letting u = 4-x^2, we get du/dx = -2x,

and if I took the second derivative of du/dx...i would get -2

this would be ideal, because I would then have du'' = -2 dx, or -1/2 du'' = dx.

So what I'm trying to ask is, if a u substitution doesn't work out clean...that is, when i take du/dx and I end up with something that doesn't help me, what exactly is stopping me from going on, that is keep taking the next derivative...just keep taking the nth derivative until eventually I end up with a constant, which I can then pull out in front of the integral. Of course, if I do this, I would have to compensate for this somehow. I am having difficulty seeing how I would compensate for this, but I have a feeling like there is an obvious compensation that could be made. Maybe take the antiderivative of the answer you get using du'' instead of du. Could I just add an another integral sign each time i differentiate u another time? that is take the antiderivative of an antiderivative as many times as i differentiate u? Maybe I would have to differentiate u again each time I take the next derivative of du/dx . Is the integral of u du the same as the integral of u' du''?

I have this feeling like I'm on to something, because if the exponent is positive, wouldn't I eventually get a constant after n differentiations? Wouldn't this make taking integrals super easy? Just differentiate n times until you get a constant, apply n compensations to the integral for doing that, and pull the constant out front. So once I figure out how to relate the integral of u du'' to u du, I will claim my nobel prize. My intuition is "if you take the derivative of du n times, just take the nth antiderivative of your answer." I just thought of it today doing my calculus 2 homework, and I became excited. We haven't learned integration by parts yet. I should sit down with a pencil and paper and test my intuition, but I'm a B student
and i suck at integrals, and USA mens hockey is on soon. Let me know if I'm on to something. Thanks!
 
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  • #2
I can't quite figure out what you are trying to do. However when changing variables for integration purposes, only the first derivative makes sense. You are replacing dx by (dx/du)du. Higher derivatives are irrelevant.
 
  • #3
I don't believe that would work. I mean you couldn't really take a second indefinite integral because you must add a constant when integrating.
 
  • #4
Try it and see... You can easily check the result of an integration problem by differentiating the answer to see if you get the original integrand.

In this case, as noted in another reply, it doesn't work.
 

1. What exactly is a U substitution approach in science?

A U substitution approach is a mathematical technique used to simplify the process of integration. It involves substituting a new variable (usually denoted as "u") for the original variable in an integral, making it easier to solve.

2. How does a U substitution approach work?

The U substitution approach works by replacing the original variable in an integral with a new variable (u) that is related to the original variable by a specific formula. This usually involves using the chain rule to rewrite the integral in terms of u, making it easier to solve.

3. Is using a U substitution approach legal in scientific research?

Yes, using a U substitution approach is a legitimate mathematical technique that is commonly used in scientific research. It is a valid method for simplifying integrals and is widely accepted in the scientific community.

4. Can a U substitution approach be used in any type of integral?

Yes, a U substitution approach can be used in most types of integrals, including definite and indefinite integrals. However, in some cases, it may not be the most efficient method and other techniques may be more suitable.

5. Are there any limitations to using a U substitution approach?

While a U substitution approach is a useful technique, it does have some limitations. It may not work for all integrals, especially those that involve trigonometric functions or other complex functions. Additionally, it may not always result in a simpler integral and other methods may be more effective.

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