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Math Help - Integration

  1. #1
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    Integration

    I've attempted this problem at least 10 times, and keep on getting the same answer, which is incorrect according to the program I have to submit it in.

    The integral given is:
    1/ (x^2 + 0 - 25)


    The answer I'm calculating is:
    (-1/10)ln(x + 5) + (1/10)ln(x-5) + C


    Any help would be great, because I am truly lost.
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by jmaillou View Post
    I've attempted this problem at least 10 times, and keep on getting the same answer, which is incorrect according to the program I have to submit it in.

    The integral given is:
    1/ (x^2 + 0 - 25)


    The answer I'm calculating is:
    (-1/10)ln(x + 5) + (1/10)ln(x-5) + C


    Any help would be great, because I am truly lost.
    what's with the 0 - 25?

    that is correct

    we got the answer from partial fractions...we write \frac 1{x^2 - 25} as \frac 1{(x + 5)(x - 5)} = \frac A{x + 5} + \frac B{x - 5} ...
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  3. #3
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    I don't know. It's an online assignment, and that's the way the question was formatted.
    And I've submitted that answer like 20 different ways into the program, and it keeps on saying that it's incorrect. So I'm thinking that I'll go talk to my prof tomorrow, because I have no clue how it's incorrect.
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  4. #4
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    They might now want you to insert the + C.

    I know that my prof lets you ignore it if you aren't doing an application question.
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by jmaillou View Post
    I don't know. It's an online assignment, and that's the way the question was formatted.
    And I've submitted that answer like 20 different ways into the program, and it keeps on saying that it's incorrect. So I'm thinking that I'll go talk to my prof tomorrow, because I have no clue how it's incorrect.
    how about \frac 1{10} (\ln (x - 5) - \ln (x + 5)) or \frac 1{10} \ln \left( \frac {x - 5}{x + 5} \right) ? with or without the C. how many tries do you get to submit it?

    i doubt they want the answer in a totally different form, which we probably would get with a trig substitution
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  6. #6
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    I've tried both of those variations, and it still says it incorrect. And I don't have to include the C term in it because it adds it automatically.

    And I get unlimited tries on this question. But it's due tomorrow.

    I just don't understand it, because the answer seems right. Maybe the 0 + 25 means something???
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  7. #7
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by jmaillou View Post
    I've tried both of those variations, and it still says it incorrect. And I don't have to include the C term in it because it adds it automatically.

    And I get unlimited tries on this question. But it's due tomorrow.

    I just don't understand it, because the answer seems right. Maybe the 0 + 25 means something???
    did you enter absolute values? tecnically it should be \frac 1{10} \ln |x - 5| - \frac 1{10} \ln |x + 5| + C
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  8. #8
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    I'm not exactly sure how to enter absolute value signs into the program.

    But I've answered other questions where ln was in the answer, and I didn't have to include any absolute value signs.
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  9. #9
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    Most of software are allowed to type abs(x+y) to yield |x+y|.
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  10. #10
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    finally!!! it worked. I just had to use absolute value signs.
    Thanks sooo much!
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  11. #11
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by jmaillou View Post
    I'm not exactly sure how to enter absolute value signs into the program.

    But I've answered other questions where ln was in the answer, and I didn't have to include any absolute value signs.
    it could depend on the problems still, for instance, if your answer was \ln (1 + e^x) then absolute value signs would not be necessary, as 1 + e^x is always positive...

    just try it and see. we're trying to figure out what the problem could be, your answer is fine (with absolute values)
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