Wednesday, 20 November 2013

`int (5x-2) / (x-2)^2 dx` Use partial fractions to find the indefinite integral

`int(5x-2)/(x-2)^2dx`


Let's use partial fraction decomposition on the integrand,


`(5x-2)/(x-2)^2=A/(x-2)+B/(x-2)^2`


`5x-2=A(x-2)+B`


`5x-2=Ax-2A+B`


comparing the coefficients of the like terms,


`A=5`


`-2A+B=-2`


Plug in the value of A in the above equation,


`-2(5)+B=-2`


`-10+B=-2`


`B=-2+10`


`B=8`


So now `int(5x-2)/(x-2)^2dx=int(5/(x-2)+8/(x-2)^2)dx`


Now apply the sum rule,


`=int5/(x-2)dx+int8/(x-2)^2dx`


Take the constant's out,


`=5int1/(x-2)dx+8int1/(x-2)^2dx`


Now let's evaluate each of the above two integrals separately,


`int1/(x-2)dx`


Apply integral substitution `u=x-2`


`=>du=dx`


`=int1/udu`


Use the common integral :`int1/xdx=ln|x|`


`=ln|u|`


Substitute back `u=x-2`


`=ln|x-2|`


Now evaluate...

`int(5x-2)/(x-2)^2dx`


Let's use partial fraction decomposition on the integrand,


`(5x-2)/(x-2)^2=A/(x-2)+B/(x-2)^2`


`5x-2=A(x-2)+B`


`5x-2=Ax-2A+B`


comparing the coefficients of the like terms,


`A=5`


`-2A+B=-2`


Plug in the value of A in the above equation,


`-2(5)+B=-2`


`-10+B=-2`


`B=-2+10`


`B=8`


So now `int(5x-2)/(x-2)^2dx=int(5/(x-2)+8/(x-2)^2)dx`


Now apply the sum rule,


`=int5/(x-2)dx+int8/(x-2)^2dx`


Take the constant's out,


`=5int1/(x-2)dx+8int1/(x-2)^2dx`


Now let's evaluate each of the above two integrals separately,


`int1/(x-2)dx`


Apply integral substitution `u=x-2`


`=>du=dx`


`=int1/udu`


Use the common integral :`int1/xdx=ln|x|`


`=ln|u|`


Substitute back `u=x-2`


`=ln|x-2|`


Now evaluate the second integral,


`int1/(x-2)^2dx`


Apply integral substitution:`v=x-2`


`dv=dx`


`=int1/v^2dv`


`=intv^(-2)dv`


Apply the power rule,


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


`=-v^(-1)`


`=-1/v`


Substitute back `v=x-2`


`=-1/(x-2)`


`:.int(5x-2)/(x-2)^2dx=5ln|x-2|+8(-1/(x-2))`


Add a constant C to the solution,


`=5ln|x-2|-8/(x-2)+C`


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