Tuesday 5 July 2016

`int x/sqrt(x^2-6x+5)` Complete the square and find the indefinite integral

`intx/sqrt(x^2-6x+5)dx`


Let's complete the square of the denominator of the integrand,


`=intx/sqrt((x-3)^2-4)dx`


Now apply integral substitution:`u=x-3`


`=>du=1dx`


`=int(u+3)/sqrt(u^2-2^2)du`


Now apply the sum rule,


`=intu/sqrt(u^2-2^2)du+int3/sqrt(u^2-2^2)du`


Now let's evaluate the first integral ,


`intu/sqrt(u^2-4)du`


Apply integral substitution:`v=u^2-4`


`=>dv=2udu`


`=int1/sqrt(v)(dv)/2`


Take the constant out and apply the power rule,


`=1/2(v^(-1/2+1)/(-1/2+1))`


`=1/2(2/1)v^(1/2)`


`=sqrt(v)`


Substitute back `v=u^2-4`


`=sqrt(u^2-4)`


Now let's evaluate the second integral,


`int3/sqrt(u^2-2^2)du`


Take the constant out,


`=3int1/sqrt(u^2-2^2)du`


Use the standard integral:`int1/sqrt(x^2-a^2)dx=ln|x+sqrt(x^2-a^2)|`


`=3ln|u+sqrt(u^2-2^2)|` ,


So add the result of the...

`intx/sqrt(x^2-6x+5)dx`


Let's complete the square of the denominator of the integrand,


`=intx/sqrt((x-3)^2-4)dx`


Now apply integral substitution:`u=x-3`


`=>du=1dx`


`=int(u+3)/sqrt(u^2-2^2)du`


Now apply the sum rule,


`=intu/sqrt(u^2-2^2)du+int3/sqrt(u^2-2^2)du`


Now let's evaluate the first integral ,


`intu/sqrt(u^2-4)du`


Apply integral substitution:`v=u^2-4`


`=>dv=2udu`


`=int1/sqrt(v)(dv)/2`


Take the constant out and apply the power rule,


`=1/2(v^(-1/2+1)/(-1/2+1))`


`=1/2(2/1)v^(1/2)`


`=sqrt(v)`


Substitute back `v=u^2-4`


`=sqrt(u^2-4)`


Now let's evaluate the second integral,


`int3/sqrt(u^2-2^2)du`


Take the constant out,


`=3int1/sqrt(u^2-2^2)du`


Use the standard integral:`int1/sqrt(x^2-a^2)dx=ln|x+sqrt(x^2-a^2)|`


`=3ln|u+sqrt(u^2-2^2)|` ,


So add the result of the two integrals,


`sqrt(u^2-4)+3ln|u+sqrt(u^2-4)|`


Substitute back `u=x-3` and add a constant C to the solution,


`=sqrt((x-3)^2-4)+3ln|x-3+sqrt((x-3)^2-4)|+C`


`=sqrt(x^2-6x+9-4)+3ln|x-3+sqrt(x^2-6x+9-4)|+C`


`=sqrt(x^2-6x+5)+3ln|x-3+sqrt(x^2-6x+5)|+C`


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