Integral Notation: Are ∫(x^2)dx & ∫dx (x^2) the Same?

In summary, there are two different types of integral notation: ∫ (expression) dx and ∫dx (expression). While they may appear different, for all intents and purposes they mean the same thing. Some physicists occasionally use the second notation, which mimics the d/dx notation for derivatives. However, the first notation is more commonly used and has a historical origin as the elongated S symbol representing the sum of all values of an expression. Both notations are valid, but using the first one provides more clarity on where the expression ends.
  • #1
DiracPool
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I'm confused over two different types of integral notation

1) ∫ (expression) dx

and

2) ∫dx (expression)

Are these the same thing?

Example: Do ∫(x^2)dx and ∫dx (x^2) mean the same thing? Or is there a difference?
 
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  • #2
Mathematicians use (1), physicists use (2). For all intents and purposes they mean the same.
 
  • #3
Great. Thanks.
 
  • #4
I'd like to change "physicists use (2)" to "some physicists use (2)" or "physicists occasionally use (2)".

I think the idea behind (2) is that it mimics the d/dx notation for derivatives. When you write ##\frac{d}{dx}ax^2##, the d/dx is like an operator that acts on ##ax^2##. Actually, it acts on the map ##x\mapsto ax^2##, not the real number ##ax^2##, and it's the x in the denominator of d/dx that let's us know that the map is ##x\mapsto x^2## rather than say ##a\mapsto x^2##.

Similarly, ##\int dx\, ax^2## is ##\int dx## acting on ##ax^2##, or to be more precise, on the map ##x\mapsto ax^2##, and now it's the x in dx that tells us that the map is ##x\mapsto ax^2## rather than e.g. ##a\mapsto ax^2##.
 
  • #5
a little history : the ∫ sign is an elongated S, which stands for sum because its the sum of all values of expression. multiply that by dt, and you get the integral
so both are valid, but personally i always use ∫f(x)dx because it tells you where the expression ends.
edit: its so typical of physicists to do this kind of stuff :P
 

FAQ: Integral Notation: Are ∫(x^2)dx & ∫dx (x^2) the Same?

What is integral notation?

Integral notation is a mathematical notation used to represent the process of finding the area under a curve on a graph. It is represented by the symbol ∫ and is often used in calculus and other areas of mathematics.

What is the difference between ∫(x^2)dx and ∫dx (x^2)?

The difference between ∫(x^2)dx and ∫dx (x^2) lies in the placement of the dx term. In the first notation, the dx term is placed after the function, indicating that the integral is being taken with respect to x. In the second notation, the dx term is placed at the end, indicating that the integral is being taken with respect to the variable of integration.

Do ∫(x^2)dx and ∫dx (x^2) always give the same result?

Yes, ∫(x^2)dx and ∫dx (x^2) will always give the same result. The placement of the dx term does not affect the outcome of the integral.

Why is the dx term necessary in integral notation?

The dx term is necessary in integral notation because it represents the variable of integration. This tells us which variable we are integrating with respect to and is crucial in determining the limits of integration.

What are some common mistakes when using integral notation?

Some common mistakes when using integral notation include forgetting to include the dx term, incorrectly placing the dx term, and not using the proper limits of integration. It is important to pay attention to the details and follow the correct notation to ensure accurate solutions.

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