# How to integrate 0 to 1 (1-x^2)^n

by mecattronics
Tags: 1x2n, integrate
 P: 2 1. The problem statement, all variables and given/known data The reduction formula is: $$\int (1-x^2)^n dx = (1-x^2)^n x + 2n \int x^2(1-x^2)^{n-1} dx$$ and the question is: use this formula above how many times is necessary to prove: $$\int^{1}_{0} (1-x^2)^n dx = 2n \frac{2(n-1)}{3} \frac{2(n-2)}{5} ... \frac{4}{2n-3} \frac{2}{(2n-1)(2n+1)}$$ but I don't know how to get there. 2. Relevant equations - 3. The attempt at a solution I tried to modify the reduction formula leaving it more recursive: $$\int (1-x^2)^n dx = (1-x^2)^n x + 2n \int x^2(1-x^2)^{n-1} dx$$ Integrating by parts: $$=x(1-x^2)^n+2n \int x^2(1-x^2)^{n-1}dx$$ let $$x^2 = -(1-x^2)+1$$ $$=x(1-x^2)^n-2n \int(1-x^2)^n dx + 2n \int (1-x^2)^{n-1}dx$$ but I still don't know how to get there with this formula. Any guidance would be appreciated.
 P: 206 use your last equality and induction.see attached. Attached Thumbnails
 P: 3,002 Since you have a definite integral perhaps you could tryparametric differentiation to get the answer. The only reference I have for this is Prof Nearings Mathematical Methods pdf at: http://www.physics.miami.edu/~nearing/mathmethods/ section 1.2 pg 4.
Emeritus
HW Helper
PF Gold
P: 7,819
How to integrate 0 to 1 (1-x^2)^n

 Quote by mecattronics 1. The problem statement, all variables and given/known data The reduction formula is:$$\int (1-x^2)^n dx = (1-x^2)^n x + 2n \int x^2(1-x^2)^{n-1} dx$$and the question is: use this formula above how many times is necessary to prove:$$\int^{1}_{0} (1-x^2)^n dx = 2n \frac{2(n-1)}{3} \frac{2(n-2)}{5} ... \frac{4}{2n-3} \frac{2}{(2n-1)(2n+1)}$$but I don't know how to get there. 2. Relevant equations 3. The attempt at a solution I tried to modify the reduction formula leaving it more recursive:$$\int (1-x^2)^n dx = (1-x^2)^n x + 2n \int x^2(1-x^2)^{n-1} dx$$Integrating by parts: $$=x(1-x^2)^n+2n \int x^2(1-x^2)^{n-1}dx$$ let $$x^2 = -(1-x^2)+1$$ $$=x(1-x^2)^n-2n \int(1-x^2)^n dx + 2n \int (1-x^2)^{n-1}dx$$ but I still don't know how to get there with this formula. Any guidance would be appreciated.

$\displaystyle \int (1-x^2)^n dx=x(1-x^2)^n-2n \int(1-x^2)^n dx + 2n \int (1-x^2)^{n-1}dx\ .$

That has $\displaystyle \ \int (1-x^2)^n dx\ \$ on both sides of the equation.

Solve for $\displaystyle \ \int (1-x^2)^n dx\ .$
P: 2
 Quote by hedipaldi use your last equality and induction.see attached.
Hi hedipaldi, thanks for your help!

How did you get this formula?
 P: 206 substitute the limits in your last equality.

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