Integrating Sin(x)/Cos^2(x) using u-substitution

  • Thread starter PauloE
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For the second integral you can substitute u = x^2 +1.In summary, the given expression can be written as the derivative of sec(x) plus a simple u substitution. The first integral requires no substitution as it is the derivative of sec(x). The second integral can be solved by substituting u = x^2 + 1.
  • #1
PauloE
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Homework Statement


[itex]∫sec(x)tan(x)+x/(x^2+1) dx[/itex]

The Attempt at a Solution


I replaced sec and tan by [itex]1/cos(x)[/itex] and [itex]sin/cos(x)[/itex] then end up with [itex]sin(x)/cos^2(x)[/itex]
then I replace [itex]cos^2 x [/itex] by [itex]1-sin^2 x [/itex] then I don't know where to go. the second part of the equation works with u substitution.
I just can't see where the identities of the first part are leading me.

any hint? thanks in advance!
 
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  • #2
PauloE said:

Homework Statement


[itex]∫sec(x)tan(x)+x/(x^2+1) dx[/itex]

The Attempt at a Solution


I replaced sec and tan by [itex]1/cos(x)[/itex] and [itex]sin/cos(x)[/itex] then end up with [itex]sin(x)/cos^2(x)[/itex]
then I replace [itex]cos^2 x [/itex] by [itex]1-sin^2 x [/itex] then I don't know where to go.

No, don't do that. Try the sub ##u = \cos x## and watch that sucker fold. :smile:
 
  • #3
you know i just used tan(x) in the first term and u substitution in the second and it worked too!

Thanks a lot!
Paulo
 
  • #4
You should ideally recognize the derivative of sec x.
 
  • #5
For the first integral you don't have to substitute anything. It is the derivative of sec(x).
 

Related to Integrating Sin(x)/Cos^2(x) using u-substitution

1. What is the integral of sec(x)tan(x)?

The integral of sec(x)tan(x) is ln|sec(x)| + C.

2. How do you solve the integral of sec(x)tan(x)?

To solve the integral of sec(x)tan(x), use the substitution method by letting u = sec(x) and du = sec(x)tan(x)dx. The integral then becomes ∫du, which is simply u + C. Substituting back in for u, the final answer is ln|sec(x)| + C.

3. Is there a shortcut for solving the integral of sec(x)tan(x)?

Yes, there is a shortcut known as the "secant-tangent shortcut." It involves rewriting the integral as ∫sec(x)tan(x)dx = ∫sec(x)sec(x)tan(x)dx, and then using the trigonometric identity sec^2(x) = 1 + tan^2(x). This simplifies the integral to ∫sec(x)(1 + tan^2(x))dx, which can be solved using the substitution method.

4. Can the integral of sec(x)tan(x) be solved using integration by parts?

Yes, the integral of sec(x)tan(x) can be solved using integration by parts. It involves letting u = sec(x) and dv = tan(x)dx, and then using the formula ∫u(x)v'(x)dx = u(x)v(x) − ∫v(x)u'(x)dx. The integral can also be solved using integration by parts twice.

5. What are some real-life applications of the integral of sec(x)tan(x)?

The integral of sec(x)tan(x) is used in various fields of science and engineering, such as physics, electrical engineering, and computer science. It is used to calculate the center of mass of a uniformly distributed wire, the moment of inertia of a rotating rod, and the power in an AC circuit. It is also used in the study of oscillatory motion and signal processing.

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