I think my problem solving is absurd.

  • Thread starter stanton
  • Start date
  • #1
74
0

Homework Statement



Evaluate the definite integral:
200911281932436339503356392025007792.jpg


Homework Equations



[tex]\int u^n du/dx[/tex] = u^(n+1)/(n+1) (n not equal to -1)


The Attempt at a Solution



(-1) muliplied by [tex]\int[/tex] (e^-x +2)^-1 (-e^-x) dx = ?

and if I follow the equation above, I got denominator zero, for I broke the rules 'n is not equal to zero'
I think I did as the equation. but now what should I do now?

200911281926416339503320196712503694.jpg
 

Answers and Replies

  • #2
statdad
Homework Helper
1,495
36
Do you know how to integrate

[tex]
\int \frac 1 u \, du
[/tex]
?
 
  • #3
327
1
Let u = e^(-x) + 2
the du = ...
 
  • #4
74
0
-e^(-x)
 
  • #5
statdad
Homework Helper
1,495
36
So with [tex] u = e^{-x} + 2 [/tex] and [tex] du = -e^{-x} [/tex], what happens to your integral?
 
  • #6
74
0
So with LaTeX Code: u = e^{-x} + 2 and LaTeX Code: du = -e^{-x} , what happens to your integral?

Thank you for your help. I did like this:

cramster-equation-20091130231296339514508975162501709.gif


cramster-equation-20091130234126339514525212662509813.gif


cramster-equation-20091130236176339514537720475008948.gif


Can you check is this the right answer?
 
  • #7
statdad
Homework Helper
1,495
36
Looks good. You are correct that the absolute value signs are not needed in the answer, since [tex] e^{-x} + 2 [/tex] is never negative.
 

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