Find the indefinite integral of [tex] \int\limits {\frac{5}{x^\frac{1}{2}+x^\frac{3}{2}} \, dx [/tex]

I have been able to simplify it to [tex] \int\limits {\frac{5\sqrt{x}}{x^3+x}} \, dx [/tex] but that is confusing,

I then did u-subsitution where [tex]u=\sqrt{x}[/tex] to obtain [tex] \int\limits {\frac{5u}{u^6+u^2}} \, dx [/tex] which simplified to [tex] \int\limits {\frac{5}{u^5+u}} \, dx [/tex], a much nicer looking integrand
however, I am still stuck

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Respuesta :

The easiest way to calculate this integral is substitution.

[tex]$\int\dfrac{5}{x^\frac{1}{2}+x^\frac{3}{2}}\,dx=5\int\dfrac{1}{x^\frac{1}{2}+(x^\frac{1}{2})^3}\,dx=5\int\dfrac{1}{\sqrt{x}+(\sqrt{x})^3}\,dx=(\star)[/tex]

Now we can substitute [tex]u=\sqrt{x}[/tex] and then:

[tex]du=\dfrac{1}{2\sqrt{x}}\,dx\qquad\implies\qquad dx=2\sqrt{x}\,du=2u\,du[/tex]

So:

[tex]$(\star)=5\int\dfrac{1}{\sqrt{x}+(\sqrt{x})^3}\,dx=5\int\dfrac{2u}{u+u^3}\,du=10\int\dfrac{1}{1+u^2}\,dx=[/tex]

[tex]=10\arctan(u)+C=\boxed{10\arctan(\sqrt{x})+C}[/tex]

Nayefx

Answer:

[tex] \displaystyle10 \tan^{-1}( \sqrt {x}^{ } ) + \rm C[/tex]

Step-by-step explanation:

we would like to integrate the following integration:

[tex] \displaystyle \int \frac{5}{ {x}^{ \frac{1}{2} } + {x}^{ \frac{3}{2} } } dx[/tex]

in order to do so we can consider using u-substitution

let our

[tex] \displaystyle u = {x}^{ \frac{1}{2} } \quad \text{and} \quad du = \frac{ {x}^{ - \frac{1}{2} } }{2} [/tex]

to apply substitution we need a little bit arrangement

multiply both Integral and integrand by 2 and ½

[tex]\displaystyle 2\int \frac{1}{2} \cdot\frac{5}{ {x}^{ \frac{1}{2} } + {x}^{ \frac{3}{2} } } dx[/tex]

factor out [tex]x^{\frac{1}{2}}[/tex]:

[tex]\displaystyle 2\int \frac{1}{2 {x}^{ \frac{1}{2} } } \cdot\frac{5}{ (1+ {x}^{ } )} dx[/tex]

recall law of exponent:

[tex]\displaystyle 2\int \frac{ {x}^{ - \frac{1}{2} } }{2 } \cdot\frac{5}{ (1+ {x}^{ } )} dx[/tex]

apply substitution:

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

rewrite x as [tex]\big(x^{\frac{1}{2}}\big)^{2}[/tex]:

[tex]\displaystyle 2\int \frac{5}{ 1+ ( {x ^{ \frac{1}{2} } })^{ 2 } } du[/tex]

substitute:

[tex]\displaystyle 2\int \frac{5}{ 1+ ( u)^{ 2 } } du[/tex]

recall integration rule of inverse trig:

[tex] \displaystyle 2 \times 5 \tan^{-1}(u)[/tex]

simplify multiplication:

[tex] \displaystyle10 \tan^{-1}(u)[/tex]

substitute back:

[tex] \displaystyle10 \tan^{-1}( {x}^{ \frac{1}{2} } )[/tex]

simplify if needed:

[tex] \displaystyle10 \tan^{-1}( \sqrt{x} )[/tex]

finally we of course have to add constant of integration:

[tex] \displaystyle10 \tan^{-1}( \sqrt {x}^{ } ) + \rm C[/tex]

and we are done!