What Is the Best Method to Integrate dx/(x*sqrt(9+16x^2))?

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In summary, for the indefinite integral dx/(x*sqrt(9+16x^2)), it is recommended to use a trigonometric substitution. After factoring out a 3 from the square root, let 4x/3 = tan(θ) and (4/3)dx = sec^2(θ)dθ. This leads to the solution of ∫(1/(3*(1+tan^2(θ))))dθ, which can then be solved using a trigonometric identity.
  • #1
cal.queen92
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Homework Statement




indefinite integral: dx/(x*sqrt(9+16x^2))


Homework Equations



Trig. Substitutions or parts??

The Attempt at a Solution



I tried using integration by parts but its got pretty messy...it also resembles a tan trig substitution, but it's within a square root. I'm stumped and can't figure out where to start...

Can anyone help?

Thanks!
 
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  • #2
Don't use integration by parts. Rewrite the problem as
[tex]\int\frac{xdx}{x^2\sqrt{9+ 16x^2}}[/tex]
and let [itex]u= 9+ 16x^2[/itex].
 
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  • #3
Factor a 3 out of [itex]\sqrt{9 +16x^2}[/itex]

[tex]\displaystyle \sqrt{9 +16x^2}=\sqrt{9\left(1+\frac{16x^2}{9}\right)}=3 \sqrt{1+\frac{16x^2}{9}}=3 \sqrt{1+\left( \frac{4x}{3} \right)^2 }[/tex]

We know that 1+tan2(θ) = sec2(θ) , so let 4x/3 = tan(θ), (4/3)dx = sec2(θ)dθ.

(I'm slow at typing, so HallsofIvy responded while I was typing. He usually has better ideas than I do. Good luck!)
 
Last edited:

Related to What Is the Best Method to Integrate dx/(x*sqrt(9+16x^2))?

1. What is the purpose of integrating dx/(x*sqrt(9+16x^2))?

The purpose of integrating dx/(x*sqrt(9+16x^2)) is to find the antiderivative or the original function from which this expression is derived. This process is useful in solving real-world problems in various fields of science and engineering.

2. What is the step-by-step process for integrating dx/(x*sqrt(9+16x^2))?

The first step is to use the substitution method by letting u = 9+16x^2 and then finding the value of du. Next, rewrite the expression as dx/(x*sqrt(u)) and use the power rule for integration to solve for the antiderivative. Finally, substitute back the original variable x to get the final answer.

3. Can this integration be solved using any other methods?

Yes, there are other methods such as using trigonometric substitution, partial fractions, or integration by parts. However, the substitution method is the most efficient and straightforward way to solve this particular expression.

4. What are the common mistakes to avoid when integrating dx/(x*sqrt(9+16x^2))?

Some common mistakes to avoid when integrating dx/(x*sqrt(9+16x^2)) include not using the correct substitution, making errors in algebraic manipulation, and forgetting to include the constant of integration. It is important to carefully follow the steps and double-check the final answer.

5. How is the solution to dx/(x*sqrt(9+16x^2)) used in real-world applications?

The solution to dx/(x*sqrt(9+16x^2)) can be used to solve problems in physics, engineering, and other fields that involve calculating the area under a curve. It can also be applied in determining the velocity of an object, the amount of work done, or the distance traveled.

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