Help Solving an Integral: I've Tried, But Can't Seem to Get It

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In summary, The integral $\displaystyle \int_{}^{} \frac{e^x}{e^{2x} + 1}\,dx$ can be solved by substituting $u = e^x$ and using the identity $\tan^{-1}{x} = \arctan{x}$. The final solution is $\arctan(e^x) + C$.
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tmt1
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I need to solve this integral. I've had this problem for about a month and I'm still not sure how to solve it:

$$\int_{}^{} \frac{e^x}{e^{2x} + 1}\,dx$$

I've tried a few methods, but I haven't gotten very far.
 
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  • #2
tmt said:
I need to solve this integral. I've had this problem for about a month and I'm still not sure how to solve it:

$$\int_{}^{} \frac{e^x}{e^{2x} + 1}\,dx$$

I've tried a few methods, but I haven't gotten very far.

Substitute $\displaystyle \begin{align*} \mathrm{e}^x = \tan{ \left( \theta \right) } \implies \mathrm{e}^x\,\mathrm{d}x = \sec^2{ \left( \theta \right) } \,\mathrm{d}\theta \end{align*}$ and the integral becomes

$\displaystyle \begin{align*} \int{ \frac{\mathrm{e}^x}{\mathrm{e}^{2\,x} + 1} \,\mathrm{d}x} &= \int{ \frac{\sec^2{ \left( \theta \right) } }{\tan^2{ \left( \theta \right) } + 1 } \,\mathrm{d}\theta } \\ &= \int{ \frac{\sec^2{ \left( \theta \right) } }{ \sec^2{ \left( \theta \right) } }\,\mathrm{d}\theta } \\ &= \int{ 1\,\mathrm{d}\theta } \\ &= \theta + C \\ &= \arctan{ \left( \mathrm{e}^x \right) } + C \end{align*}$
 
  • #3
tmt said:
$$\int_{}^{} \frac{e^x}{e^{2x} + 1}\,dx$$

[tex]\text{Let }\,u = e^x \quad\Rightarrow\quad du \,=\,e^x\,dx[/tex]

[tex]\text{Substitute: }\;\int \frac{du}{u^2+1}[/tex]

[tex]\text{Integrate: }\; \arctan u + C[/tex]

[tex]\text{Back-substitute: }\;\arctan(e^x) + C [/tex]
 

FAQ: Help Solving an Integral: I've Tried, But Can't Seem to Get It

1. How do I approach solving an integral?

Solving integrals requires a combination of understanding the basic rules of integration and having a good grasp of algebraic manipulation. It is important to first simplify the integrand and then use integration techniques such as substitution, integration by parts, or trigonometric identities.

2. What should I do if I get stuck while solving an integral?

If you are unable to solve an integral, try breaking it down into smaller parts and solving them individually. It may also be helpful to consult a textbook or online resources for additional examples and techniques. Don't be afraid to ask for help from a teacher or tutor.

3. How do I know which integration technique to use?

The choice of integration technique depends on the complexity of the integrand. Generally, substitution is used for integrals involving nested functions, integration by parts is used for products of functions, and trigonometric identities are used for integrals involving trigonometric functions.

4. Are there any common mistakes to avoid while solving integrals?

Some common mistakes to avoid while solving integrals include forgetting to add a constant of integration, using the wrong integration technique, and making calculation errors. It is important to double check your work and use proper notation when solving integrals.

5. How can I improve my skills in solving integrals?

The best way to improve your skills in solving integrals is through practice. Try solving a variety of integrals and make sure to understand the steps involved in each solution. It can also be helpful to review the fundamental rules of integration and seek help from a teacher or tutor if needed.

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