Indefinite integral of arcsec(x)

In summary, the conversation discusses finding the integral of arcsec(x) and the steps involved in solving it. The conversation also mentions checking the answer with Wolfram Alpha and concludes that both the given answer and Wolfram's answer are correct, just manipulated differently due to the constant of integration.
  • #1
PWiz
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Just for fun, I tried this rather trivial problem, but I think I went wrong somewhere:
$$\int arcsec(x) \ dx$$
Let ##arcsec(x)=y## . Then ##x=sec \ y##, or ##y=arccos(\frac 1{x})##
So the problem becomes $$\int arccos(\frac 1 {x}) \ dx$$
Let ##\frac 1 {x} = cos \ u## , so that ##dx = secu \ tanu \ du##.
So the questions simplifies to ##\int u \ secu \ tanu \ du##. If I integrate by parts, then this equals to
$$u \int secu \ tanu \ du - \int (\int secu \ tanu \ du) du$$
Since ##\int secu \ tanu \ du = secu##, I get ##u \ secu - \int secu \ du##
##\int secu \ du = ln(\sqrt{\frac{1+sinu}{1-sinu}})##
Substituting the Xs, I get $$x \ arcsec(x) - ln(\sqrt{\frac{1+\sqrt{1-\frac{1}{x^2}}}{1-\sqrt{1-\frac{1}{x^2}}}}) + c= x \ arcsec(x) - ln(\sqrt{\frac{x+\sqrt{x^2-1}}{x-\sqrt{x^2-1}}}) + c $$
where ##c## is an arbitrary constant. I checked my answer with Wolfram Alpha here:
http://integrals.wolfram.com/index.jsp?expr=arcsec(x)&random=false
As you can clearly see, the answer is different from mine. In which step did I goof?
 
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  • #2
PWiz said:
, I get $$x \ arcsec(x) - ln(\sqrt{\frac{1+\sqrt{1-\frac{1}{x^2}}}{1-\sqrt{1-\frac{1}{x^2}}}}) + c= x \ arcsec(x) - ln(\sqrt{\frac{x+\sqrt{x^2-1}}{x-\sqrt{x^2-1}}}) + c $$
where ##c## is an arbitrary constant. I checked my answer with Wolfram Alpha here:
http://integrals.wolfram.com/index.jsp?expr=arcsec(x)&random=false
As you can clearly see, the answer is different from mine. In which step did I goof?
Your all steps are correct, you have not goofed.
Wolfram's answer as well as your answer is correct. It's the way of manipulating.
Rearrange some terms in wolfram' answer and in yours. You will see both are same.

Edit [ Add] indefinite integration is an area where you get answers which are not matching by someone's else. The constant of integration has a big role here.
 
  • #3
Okay, thanks!
 

Related to Indefinite integral of arcsec(x)

What is the indefinite integral of arcsec(x)?

The indefinite integral of arcsec(x) is ∫arcsec(x) dx = ln|sec(x) + tan(x)| + C

What is the domain of the indefinite integral of arcsec(x)?

The domain of the indefinite integral of arcsec(x) is (-∞, -1] ∪ [1, ∞)

How do you solve the indefinite integral of arcsec(x)?

To solve the indefinite integral of arcsec(x), use the trigonometric identity sec^2(x) = 1 + tan^2(x) and substitute u = tan(x). This will result in an integral of the form ∫(1 + u^2)^(-1/2) du, which can be solved using the substitution method.

Can the indefinite integral of arcsec(x) be expressed in terms of elementary functions?

No, the indefinite integral of arcsec(x) cannot be expressed in terms of elementary functions. It can only be expressed in terms of non-elementary functions such as logarithms.

What is the derivative of the indefinite integral of arcsec(x)?

The derivative of the indefinite integral of arcsec(x) is sec(x).

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