drwls & Damon - maths

hey guys,

i follow you up to the point of intergrating the final line. How would I intergrate [x^-2.e^-x] dx

thx

  1. 👍 0
  2. 👎 0
  3. 👁 47
  1. My first suggestion was to try the method of "integration by parts", but that may not work. I found a recursion formula for the integral in my Table of Integrals, but it ends up requiring the integral of e^-x/x , which is a new fucntion called the exponential integral, Ei(x). Perhaps I made a mistake somewhere applying the "integrating factor" method. Damon has made more progress and is better equipped to help you. I am giving up on it

    1. 👍 0
    2. 👎 0
    posted by drwls
  2. Yes, use the recursion formula. You need it later to cancel the next term.

    in general:
    int e^ax dx/x^n = (1/(n-1)) [-e^ax/x^(n-1) + a int e^ax/x^(n-1)dx] for n integergreater than one
    here n is two
    so here I had:
    y e^-x/x=int( e^-x dx/x)(1/x + 1)dx + C

    ye^-x/x =int e^-x dx/x^2 + int e^-x dx/x
    +C

    ye^-x / x = (1/1)[-e^-x/x - int e^-x dx/x ] + e^-x dx/x +C
    see that gets rid of the int e^-x dx/x terms and you are left with
    y e^-x/x = -e^-x/x + C
    y = -1 + x C / e^-x
    y = x C e^x - 1 :)

    1. 👍 0
    2. 👎 0
    posted by Damon
  3. Typo:

    ye^-x / x = (1/1)[-e^-x/x - int e^-x dx/x ] + INTEGRAL e^-x dx/x +C
    see that gets rid of the int e^-x dx/x terms and you are left with

    1. 👍 0
    2. 👎 0
    posted by Damon

Respond to this Question

First Name

Your Response

Similar Questions

  1. physics

    hey you guys , i reay appreciate it if you guys help me out . Q: a vector is a physica quantity that has which of the following properties ( can be more than one) a)magnitude b)color c)speed d)direction

    asked by kevin on April 12, 2012
  2. English

    Hey guys, I was just wondering if you could help me find or explain to me media influence in the Hunger Games. I know this is a big part of the story, but I really need clarification. Thanks a lot guys!

    asked by Alex on January 13, 2011
  3. Economics 101

    Hey guys my Econ final is on Tuesday and I could use some help. These are 4 example questions true/false with explanation needed. 1. A monopolist will produce less and charge a higher price than a perfectly competitive industry.

    asked by Zach on May 4, 2008
  4. English

    Hey guys I have an essay i need to write next week, and my english teacher is giving us 5 classes to do it in. Needs to be 900-1200 words, and we are allowed to bring in a sheet with some points and ideas about the topic, so we

    asked by Melih on May 8, 2009
  5. Language

    Read the poem and answer the questions that follow 1.There once was a cowboy named Ray 2. Who never had that much to say, 3. Except for the times 4. Stampedes stopped on a dime 5. When that cowboy named Ray hollered Hey 1.in which

    asked by Matthew on May 10, 2013
  6. Art Question

    When children draw cross-sections of plants, they are: 1. intergrating science and art (Or) 2. intergrating mathematics and science Lordy. Surely you have some thinking on this, this question hardly stimulates the cerebral cortex.

    asked by Kendra--Please Help!! on March 31, 2007
  7. english

    hey people!! im new here and i just got an essay to do on english altough its the first day of school!! please guys i really need your help.. its a essay on the following topics: 1-summer 2-love is not all it's made out to be 3-a

    asked by wayne on January 21, 2009
  8. Calc

    Find the point on the line –2x+2y–3=0 which is closest to the point (–4–4). Please provide solution. ( , ) Thanks guys!

    asked by Issac on March 15, 2014
  9. Geometry

    For each property listed from plane Euclidean geometry, write a corresponding statement for non-Euclidean spherical geometry. A line segment is the shortest path between two points Hey guys I want to know how to do this and can

    asked by Anonymous on May 29, 2011
  10. Pencils

    Hey guys, I know this is a homework site, but I cant seem to find this anywhere on the web. I cant seem to find this pencil my chemistry teacher suggested to get, since I'm on the chem league, we will be doing a lot of Multiple

    asked by Jackie on October 26, 2008

More Similar Questions