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Math Help - Can someone help me with this problem

  1. #1
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    Can someone help me with this problem

    (e^x/10 - x^2 - 1)dx {5
    {-5
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  2. #2
    MHF Contributor Mathstud28's Avatar
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    Quote Originally Posted by 10164064 View Post
    (e^x/10 - x^2 - 1)dx {5
    {-5
    With my super amazing mind-reading ablilities...this reads

    \int_{-5}^{5}e^{\frac{x}{10}}-x^2-1~~dx

    Well I will compute the antiderivative and you do the definite part

    \int{e^{\frac{x}{10}}~dx}=10\int{u}~du=10e^{\frac{  x}{10}}

    Now what substitution did I make?

    \int{x^2}~dx=\frac{x^3}{3}\longleftarrow\text{no surprises here}

    \int~dx=x\longleftarrow\text{none here either}
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  3. #3
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    right i got that part but when I plug in the 5 and -5 I keep getting a negative answer when i subtract it
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  4. #4
    MHF Contributor Mathstud28's Avatar
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    Quote Originally Posted by 10164064 View Post
    right i got that part but when I plug in the 5 and -5 I keep getting a negative answer when i subtract it
    The answer is negative.
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  5. #5
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    Ok thank you I just thought I was doing something wrong
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  6. #6
    MHF Contributor Mathstud28's Avatar
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    Quote Originally Posted by 10164064 View Post
    Ok thank you I just thought I was doing something wrong
    Well since

    \int_a^{b}f(x)~dx=F(b)-F(a) it is easily assumable that an integral can assume a negative value.
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  7. #7
    Grand Panjandrum
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    Quote Originally Posted by 10164064 View Post
    (e^x/10 - x^2 - 1)dx {5
    {-5
    Use brackets to make your meaning clear:

    Something like:

    integral [e^(x/10) - x^2 - 1] dx from -5 to 5

    RonL
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