My Beta Functions - Part 2

Calculus Level 4

What is

0 1 x m 1 ( 1 x p ) n 1 d x ? \large \displaystyle \int_{0}^{1} x^{m-1} (1-x^p)^{n-1} dx \ ?

Check this wiki on beta function
Try my set
p β ( m p , n ) p \beta(\frac{m}{p},n) 1 p β ( m , n p ) \frac{1}{p} \beta(m,np) 1 p β ( m p , n ) \frac{1}{p} \beta(mp,n) 1 p β ( m p , n ) \frac{1}{p} \beta(\frac{m}{p},n)

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1 solution

Let the given integral be I I

Take the substitution x p = t . . . . . ( 1 ) x^p = t ..... (1)

Differentiate ( 1 ) (1)

d x p x p 1 = d t d x p x p x = d t d x p t t 1 p = d t d x p t p 1 p = d t d x = d t p t p 1 p dx px^{p-1} = dt \Rightarrow dx p \frac{x^p}{x} = dt \Rightarrow dx p \frac{t}{t^{\frac{1}{p}}} = dt \Rightarrow dx p t^{\frac{p-1}{p}} = dt \Rightarrow dx = \dfrac{dt}{p t^{\frac{p-1}{p}}}

I = 1 p 0 1 t m 1 p t p 1 p ( 1 t ) n 1 d t I = \displaystyle \frac{1}{p} \int _{0}^{1} \dfrac{t^{\frac{m-1}{p}}}{t^{\frac{p-1}{p}}} (1-t)^{n-1} dt

1 p 0 1 t m p p ( 1 t ) n 1 d t \displaystyle \Rightarrow \frac{1}{p} \int_{0}^{1} t^{\frac{m-p}{p}} (1-t)^{n-1} dt

1 p 0 1 t m p 1 ( 1 t ) n 1 d t \displaystyle \Rightarrow \frac{1}{p} \int _{0}^{1} t^{\frac{m}{p}-1} (1-t)^{n-1} dt

Which is 1 p β ( m p , n ) \frac{1}{p} \beta(\frac{m}{p} ,n)

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