how to integrate    ( x^2+2x+2)/(x^3 e^x)  

Expert Answers

An illustration of the letter 'A' in a speech bubbles

You need to use the linearity of integrals such that:

`int  (x^2+2x+2)/(x^3 e^x) dx = int (x^2)/(x^3)e^(-x)dx + int (2x)/(x^3)*e^(-x)dx + int 2/x^3 e^(-x)dx`

`int (x^2+2x+2)/(x^3 e^x) dx = int 1/x e^(-x)dx + 2 int 1/x^2 e^(-x)dx + 2 int 1/x^3 e^(-x)dx`

You need to use integration by parts to solve `int 1/x e^(-x)dx` such that:

`int udv = uv - int vdu`

`u = 1/x => du = -1/x^2`

`dv = e^(-x) => v = -e^(-x)`

`int 1/x e^(-x)dx = -e^(-x)/x - int 1/x^2 e^(-x) dx`

`int (x^2+2x+2)/(x^3 e^x) dx = -e^(-x)/x - int 1/x^2 e^(-x) dx + 2 int 1/x^2 e^(-x)dx + 2 int 1/x^3 e^(-x)dx`

`int (x^2+2x+2)/(x^3 e^x) dx = -e^(-x)/x + int 1/x^2 e^(-x)dx + 2 int 1/x^3 e^(-x)dx `

You need to use integration by parts to solve `int 1/x^3 e^(-x)dx`  such that:

`int 1/x^3 e^(-x)dx = -1/(2x^2) e^(-x) - (1/2)int 1/x^2 e^(-x)dx `

`u = e^(-x) => du = -e^(-x)`

`dv = 1/x^3 => v = -1/(2x^2)`

`int (x^2+2x+2)/(x^3 e^x) dx = -e^(-x)/x + int 1/x^2 e^(-x)dx -1/(x^2) e^(-x) - int 1/x^2 e^(-x)dx`

Reducing like terms yields:

`int (x^2+2x+2)/(x^3 e^x) dx = -e^(-x)/x -1/(x^2) e^(-x) + c`

`int (x^2+2x+2)/(x^3 e^x) dx = -e^(-x)/x(1 + 1/x) + c`

Hence, evaluating the given integral, using mostly integration by parts, `int (x^2+2x+2)/(x^3 e^x) dx = -e^(-x)/x(1 + 1/x) + c.`

See eNotes Ad-Free

Start your 48-hour free trial to get access to more than 30,000 additional guides and more than 350,000 Homework Help questions answered by our experts.

Get 48 Hours Free Access
Approved by eNotes Editorial Team