Evaluate Integral Homework: 5*ln(x^2+1) + ?

  • Thread starter danielatha4
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In summary: If not, you should definitely try it. It can be a bit more involved, but it can be very helpful in solving integrals.In summary, the student attempted to solve an integral by using a trig substitution, but they may not have been successful because they haven't learned how to use trig substitutions yet.
  • #1
danielatha4
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Homework Statement


Evaluate [tex]\int[/tex][tex]\frac{5x+5}{x^2+1}[/tex]


Homework Equations





The Attempt at a Solution


5*[tex]\int[/tex][tex]\frac{x+1}{x^2+1}[/tex]

5*[tex]\int[/tex][tex]\frac{x}{x^2+1}[/tex]+[tex]\int[/tex][tex]\frac{1}{x^2+1}[/tex]

The first term's value is (1/2)ln(x2+1) but what is the second term?
 
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  • #2
for the second term, consult a table of integrals
 
  • #3
arctan(x)
Don't forget that both antiderivatives are multiplied by 5, and don't forget your constant of integration.
 
  • #4
We were never instructed to refer to any tables, and I don't suspect that we should have to. And we haven't done anything as complex as arctan(x) yet.

The method to evaluate the integral should be fairly simple. It's the beginning of a calculus 2 class.
 
  • #5
Yes well that doesn't really change the fact that the antiderivative of 1/(1+x^2) is arctan(x) does it? And arctan(x) is not that complex, it's actually quite simple.
 
  • #6
I'm not doubting that the antiderivative of 1/(x^2+1) is arctan(x). That's just not the method my teacher wants me to use because haven't learned inverse trig functions yet. Maybe I went about the problem the wrong way from the beginning?
 
  • #7
danielatha4 said:
I'm not doubting that the antiderivative of 1/(x^2+1) is arctan(x). That's just not the method my teacher wants me to use because haven't learned inverse trig functions yet. Maybe I went about the problem the wrong way from the beginning?

You did it exactly right. If you don't know the antiderivative is arctan(x) then you have to derive it using a trig substitution. Put x=tan(u).
 
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  • #8
danielatha4 said:
We were never instructed to refer to any tables, and I don't suspect that we should have to. And we haven't done anything as complex as arctan(x) yet.

The method to evaluate the integral should be fairly simple. It's the beginning of a calculus 2 class.
You probably did learn how to differentiate arctan(x) last semester. If you recognized the integrand was the derivative, you could just write the answer down for the second integral.

Have you learned using trig substitutions to do integrals yet?
 

FAQ: Evaluate Integral Homework: 5*ln(x^2+1) + ?

What is the integral of 5*ln(x^2+1)?

The integral of 5*ln(x^2+1) is equal to x^2*ln(x^2+1) + 2x + C.

How do I evaluate the integral 5*ln(x^2+1)?

To evaluate this integral, you can use the substitution method. Let u = x^2+1, then du/dx = 2x and dx = du/2x. Substituting these values into the integral, we get 5*ln(u)*(du/2x). Simplifying further, we get 5*ln(u)/2 + C = 5*ln(x^2+1)/2 + C.

Can the integral 5*ln(x^2+1) be solved using integration by parts?

Yes, the integral 5*ln(x^2+1) can be solved using integration by parts. Let u = ln(x^2+1), then du/dx = 2x/(x^2+1) and v = 5x, then dv/dx = 5. Substituting these values into the integration by parts formula, we get the final result of x^2*ln(x^2+1) + 2x + C.

What is the antiderivative of 5*ln(x^2+1)?

The antiderivative of 5*ln(x^2+1) is equal to x^2*ln(x^2+1) + 2x + C.

Can the integral 5*ln(x^2+1) be evaluated using substitution and integration by parts together?

Yes, the integral 5*ln(x^2+1) can be evaluated using a combination of substitution and integration by parts. This method is known as the double-substitution method and involves using substitution first, followed by another substitution or integration by parts to simplify the integral further.

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