# More of a math problem, but from a physics text

• David92
In summary, the conversation discusses a problem with understanding how to remove the imaginary part in a mathematical expression. The solution involves using the identity eiθ = cos(θ)+i*sin(θ) and exploiting the evenness of the cosine function. The person providing guidance also points out that the final answer is real, so the imaginary part can be ignored.
David92

## Homework Statement

[/B]
So I can't get from line (53) to line (54)

I do not understand how interchanging the variables will cause the imaginary part to disappear

## The Attempt at a Solution

I'm not sure where to start
I know exp(ix) = cos(x) +isin(x)
And the only way i see cos(x) coming out is using the exponential identity
exp(ix) + exp(-ix) = 2cos(x) (but this clearly isn't it)
But this 'interchanging' variables really doesn't make sense to me

David92 said:

## Homework Statement

View attachment 113014 [/B]
So I can't get from line (53) to line (54)
From the identity e = cos(θ)+i*sin(θ), you can split the real and imaginary parts of the integral. You also know that the cosine is an even function, so cos(-θ) = cos(θ) is used to remove the negative exponent.
I do not understand how interchanging the variables will cause the imaginary part to disappear
You are over-thinking it. That is not what makes the imaginary part disappear. If you know that the final answer is real, then you know that the imaginary part is zero without having to do anything. So just ignore the sin terms.

Last edited:
Oh wow you are right I was overthinking it. Thinking in terms of even and odd functions really helped, thanks!

## 1. What is the difference between a math problem and a physics problem?

A math problem is a question or statement that requires the use of mathematical skills to solve, while a physics problem involves applying physical principles and theories to a real-world scenario.

## 2. How does solving math problems help with understanding physics?

Math is the language of physics, so understanding mathematical concepts and equations is crucial for understanding and solving physics problems. It allows us to quantify and analyze physical phenomena.

## 3. Can you provide an example of a physics problem that involves math?

An example of a physics problem that involves math is calculating the acceleration of an object rolling down an inclined plane. This requires using equations from both physics (such as Newton's second law) and math (such as trigonometry).

## 4. How do you approach solving a math problem from a physics text?

The first step is to carefully read and understand the problem, including any given information and what is being asked. Then, identify relevant equations and concepts from physics that can be used to solve the problem. Finally, use mathematical skills to manipulate the equations and solve for the unknown quantities.

## 5. What are some tips for effectively solving math problems in a physics text?

Some tips for solving math problems in a physics text include:

• Practice regularly and review mathematical concepts and techniques frequently.
• Draw diagrams or make sketches to visualize the problem.
• Break down the problem into smaller, more manageable parts.
• Check your units and ensure they are consistent throughout the problem.
• Double-check your calculations and make sure your answer makes sense in the context of the problem.

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