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Math Help - Differentiation

  1. #1
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    Differentiation

    Hi i need to differentiate the following function:

    f(x) = e^x . (x+2) . (x-1)

    I know the answer is

    f'(x) = e^x (x^2 + 3x -1)

    But have no idea how to get to this! Any help please?
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  2. #2
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    Plus then i need to make f'(x) = 0 and find that x = -3.30 and x = 0.30 :\
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  3. #3
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    I think the function looks like this:

    f(x)=e^{x(x+2)(x-1)}

    If I'm correct, then the derivative is f'(x)=e^u\frac{du}{dx} where u=x(x+2)(x-1). This is the chain rule.

    It's difficult to read what you typed. You should try to use the latex.
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  4. #4
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    No sorry the question is

    f(x) = (e^x) . (x+2) . (x-1)

    and answer is

    f'(x) = (e^x) (x^2 + 3x -1)
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  5. #5
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    If the equation is f(x) = e^x (x+2) (x-1)

    Then f'(x) =\left[e^x \right]' (x+2) (x-1) +e^x \left[(x+2) (x-1)\right]'
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  6. #6
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    Thanks for everyones help ive got it sorted now!

    Need help with this now!

    Whats the derivative of:

    Sin ( (x^2) + x )
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  7. #7
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    Lets say

     y = \sin( x^2 + x ) and u = x^2 + x\implies y=\sin(u)

    Now \frac{dy}{dx} = \frac{dy}{du}\times \frac{du}{dx}
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  8. #8
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    so the answer is..

    (2x + 1) . cos( (x^2) + x )

    Is that right?
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  9. #9
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    Okay so i swear the answer to this question is wrong!

    Bit of integration instead of differentiation!

    \int3xsin(7-x) dx

    and the answer is

    3xcos(7-x) + 3sin(7-x) + c

    Whereas I would have said it was

    3xsin(7-x) - 3cos(7-x) + c

    Any help?
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  10. #10
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    Quote Originally Posted by xxJaRxx View Post
    so the answer is..

    (2x + 1) . cos( (x^2) + x )

    Is that right?
    Good work!
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  11. #11
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    Quote Originally Posted by xxJaRxx View Post
    Okay so i swear the answer to this question is wrong!

    Bit of integration instead of differentiation!

    \int3xsin(7-x) dx

    and the answer is

    3xcos(7-x) + 3sin(7-x) + c

    Whereas I would have said it was

    3xsin(7-x) - 3cos(7-x) + c

    Any help?
    Read this Integration by parts - Wikipedia, the free encyclopedia

    For \int uv' = uv - \int vu'

    In your case make u=3x and v' = \sin(7-x)

    now find u' and v
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