Variable change in definite integration

In summary, a variable change in definite integration is a technique used to simplify and solve integrals. It is used to make the integrand easier to integrate and can transform the limits of integration. To perform a variable change, a new variable is substituted into the integral and the limits are adjusted accordingly. The benefits of using variable change include simplifying the integrand, making the integral more solvable, and revealing new insights. However, there are limitations to using this technique, such as the possibility of introducing more complicated integrals or difficult to evaluate limits. Careful consideration is necessary before applying variable change in definite integration.
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bartrocs
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I am having trouble understanding how the author of the textbook "Physics for scientists and engineers" (Randall D Knight), is performing the variable change in the definite integral of the picture that I have taken a screen clipping of. Can someone please help me figure this out?
 

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Variable r is being replaced by variable u where

u = z[itex]^{2}[/itex] + r[itex]^{2}[/itex].

Hence

[itex]\frac{du}{dr}[/itex] = 2r

since z is a constant.
 
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thanks! I understand now
 

1. What is a variable change in definite integration?

A variable change in definite integration is a mathematical technique used to simplify and solve integrals by replacing the variable of integration with a new variable. This allows for easier integration and can help to find the solution of more complex integrals.

2. Why is variable change used in definite integration?

Variable change is used in definite integration to simplify the integrand and make it easier to integrate. It can also help to transform the limits of integration and make the integral more solvable. It is particularly useful in cases where the original variable is difficult to integrate or the integral involves multiple variables.

3. How do you perform a variable change in definite integration?

To perform a variable change in definite integration, you need to first determine the new variable to use. This can be done by considering the integrand and finding a suitable substitution that will simplify the integral. Then, you can substitute the new variable into the integral and change the limits of integration accordingly. Finally, solve the integral using the new variable.

4. What are the benefits of using variable change in definite integration?

There are several benefits of using variable change in definite integration. It can help to simplify the integrand and make it easier to integrate, especially in cases where the original variable is difficult to integrate. It can also help to transform the limits of integration and make the integral more solvable. Additionally, variable change can also reveal new insights and relationships between different mathematical concepts.

5. Are there any limitations to using variable change in definite integration?

While variable change can be a powerful tool in solving integrals, it may not always be applicable or appropriate. In some cases, the new variable may not simplify the integral or may even make it more complicated. Additionally, the substitution may also introduce new limits of integration that are difficult to evaluate. It is important to carefully consider the integral and the chosen variable substitution before proceeding with a variable change in definite integration.

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