Sunday 13 July 2014

`int 1 / (sqrt(x)sqrt(1-x)) dx` Find the indefinite integral

Recall  that `int f(x) dx = F(x) +C `  where:


f(x) as the integrand function


F(x) as the antiderivative of f(x)


C as the constant of integration..


 For the given problem, the integral: `int 1/(sqrt(x)sqrt(1-x))dx`


does not yet resemble any formula from table of integrals.


To evaluate this, we have to apply u-substitution by letting:


`u =sqrt(x)`


Square both sides: `(u)^2=(sqrt(x))^2` , we get: `u^2 =x`


Then plug-in `u^2 =x` in `sqrt(1-x)` :


` sqrt(1-x) =...

Recall  that `int f(x) dx = F(x) +C `  where:


f(x) as the integrand function


F(x) as the antiderivative of f(x)


C as the constant of integration..


 For the given problem, the integral: `int 1/(sqrt(x)sqrt(1-x))dx`


does not yet resemble any formula from table of integrals.


To evaluate this, we have to apply u-substitution by letting:


`u =sqrt(x)`


Square both sides: `(u)^2=(sqrt(x))^2` , we get: `u^2 =x`


Then plug-in `u^2 =x` in `sqrt(1-x)` :


` sqrt(1-x) = sqrt(1-u^2)` .


Apply implicit differentiation on `u^2 =x` , we get: `2u du = dx` .


Plug-in `sqrt(x) =u` , `sqrt(1-x) = sqrt(1-u^2)` , and `dx= 2u du` , we get:


`int 1/(sqrt(x)sqrt(1-x))dx =int 1/(u*sqrt(1-u^2))*(2u du)`


                        ` =int (2u du)/(usqrt(1-u^2))`


 Cancel out common factor u:


`int 1/(usqrt(1-u^2))*(2u du)=int (2 du)/sqrt(1-u^2)`


Apply the basic integration property: `int c*f(x) dx = c int f(x) dx` :


`int(2 du)/(sqrt(1-u^2))= 2int(du)/sqrt(1-u^2)`


The integral part resembles the basic integration formula for inverse sine function:


`int (du)/sqrt((a^2 -u^2)) = arcsin(u/a) +C`


Then,


`2int(du)/sqrt(1-u^2) =2arcsin(u/1) +C`


                   ` =2 arcsin(u) +C`


Express it in terms of x by plug-in `u =sqrt(x)` for the final answer :


`int 1/(sqrt(x)sqrt(1-x))dx =2 arcsin(sqrt(x)) +C`

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