Proving Integral of (1+x^2)^n: Techniques and Examples

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In summary, the given equation \int \frac{dx}{(1+x^2)^n} \;=\; \frac{1}{2(n-1)}\cdot\frac{x}{(1+x^2)^{n-1}} - \frac{2n-3}{2(n-1)}\int \frac{dx}{(1+x^2)^{n-1}} is asking for a proof and can be solved using integration by parts without induction. The solution involves making In+1 the subject and lowering each term by 1.
  • #1
Alexx1
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[tex]\int \frac{dx}{(1+x^2)^n} \;=\; \frac{1}{2(n-1)}\cdot\frac{x}{(1+x^2)^{n-1}}
\;\;-\;\; \frac{2n-3}{2(n-1)}\int \frac{dx}{(1+x^2)^{n-1}}[/tex]

Can someone prove this?
 
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  • #2
Alexx1 said:
[tex]\int \frac{dx}{(1+x^2)^n} \;=\; \frac{1}{2(n-1)}\cdot\frac{x}{(1+x^2)^{n-1}}
\;\;-\;\; \frac{2n-3}{2(n-1)}\int \frac{dx}{(1+x^2)^{n-1}}[/tex]

Can someone prove this?

What is the context of your question? Is it for schoolwork/homework?
 
  • #3
berkeman said:
What is the context of your question? Is it for schoolwork/homework?

I have exam (university) January 15th and we have exercises but we don't have answers.. so I would lik to know how to solve this one
 
  • #4
Alexx1 said:
I have exam (university) January 15th and we have exercises but we don't have answers.. so I would lik to know how to solve this one

Okay. Schoolwork needs to go in the Homework Help forums, and you need to show some effort on trying to solve it. I'll move the thread now. Can you say anything about potential ways to solve the problem?
 
  • #6
Alexx1 said:
[tex]\int \frac{dx}{(1+x^2)^n} \;=\; \frac{1}{2(n-1)}\cdot\frac{x}{(1+x^2)^{n-1}}
\;\;-\;\; \frac{2n-3}{2(n-1)}\int \frac{dx}{(1+x^2)^{n-1}}[/tex]

Can someone prove this?

Have you try [tex]x=tan(\theta)[/tex]

[tex]1+tan^{2}(\theta)=sec^{2}(\theta)[/tex]
 
Last edited:
  • #7
I think you made a mistake typing it: It should be '+' in between the 2 fraction and the integral.

Just do a simple Integration by parts without induction.

Let dv=dx , u = 1/(1+x2)n

In = x/(1+x2)n + 2n(integral)[x2/(1+x2)n+1]dx

as 'x2 = 1 + x2 - 1',

You should end up with: In = x/(1+x2)n + 2n(In - In+1)

Make In+1 the subject. Finally lower each of the n terms by 1. (so n+1 -> n, and n -> n-1)
 

1. What is the basic technique for proving the integral of (1+x^2)^n?

The basic technique for proving the integral of (1+x^2)^n is to use the binomial theorem to expand the expression into a sum of terms, and then apply the power rule for integration to each term.

2. Can the integral of (1+x^2)^n be evaluated using substitution?

Yes, the integral of (1+x^2)^n can be evaluated using substitution. In particular, the substitution u = 1+x^2 can be used to transform the integral into a form that can be integrated using the power rule.

3. Are there any special cases to consider when proving the integral of (1+x^2)^n?

Yes, there are two special cases to consider when proving the integral of (1+x^2)^n. The first is when n = -1, in which case the integral will involve a natural logarithm. The second is when n is a negative integer, in which case the integral will involve a rational function.

4. How can the integral of (1+x^2)^n be used to calculate the area under a curve?

The integral of (1+x^2)^n can be used to calculate the area under a curve by setting up the integral as the difference between the antiderivative evaluated at the upper and lower limits of integration. This will give the area between the curve and the x-axis.

5. Can the integral of (1+x^2)^n be evaluated using integration by parts?

Yes, the integral of (1+x^2)^n can be evaluated using integration by parts, but it may not lead to a simpler expression. In most cases, using the binomial theorem and the power rule will be a more efficient method for evaluating the integral.

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