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    Am I using the product rule correct to work this out?
    dy/dx = 4x^2e^(-5x)
    so its 8xe^(-5x)+4x^2-5e^(-5x)
    so 8xe^(-5x)-20x^2e^(-5x)
    Im not sure if I simplified it correctly. Also am I right in thinking the product rule and the formula you use for integration by parts are different?

    For some reason I am unable to post in the math study help section.
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    Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.

    You can also find the Exam Thread list for A-levels here and GCSE here. :dumbells:


    Just quoting in Puddles the Monkey so she can move the thread if needed
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    (Original post by Puddles the Monkey)
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    (Original post by dont)
    Am I using the product rule correct to work this out?
    dy/dx = 4x^2e^(-5x)
    so its 8xe^(-5x)+4x^2-5e^(-5x)
    so 8xe^(-5x)-20x^2e^(-5x)
    Im not sure if I simplified it correctly. Also am I right in thinking the product rule and the formula you use for integration by parts are different?

    For some reason I am unable to post in the math study help section.
    Yeah, different formulae, so dy/dx = u(dv/dx) + v(du/dx) with the product rule

    d/dx(4x2e-5x) = 4x2(-5e-5x) + e-5x(8x) = 8xe-5x - 20x2e-5x
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    (Original post by dont)
    Am I using the product rule correct to work this out?
    Yes.

    dy/dx = 4x^2e^(-5x)
    so its 8xe^(-5x)+4x^2-5e^(-5x)
    so 8xe^(-5x)-20x^2e^(-5x)


    Im not sure if I simplified it correctly.
    To simplify it further, pull out the exponential as a common factor: e^{-5x}(8x - 20x^2) = 4xe^{-5x}(2 - 5x)

    Also am I right in thinking the product rule and the formula you use for integration by parts are different?
    Well, you derive IBP from the product rule, so meh. I wouldn't really call them different, you're just rearranging an equation.

    (Original post by Alexion)
    Yeah, different formulae, so dy/dx = u(dv/dx) + v(du/dx) with the product rule

    d/dx(4x2e-5x) = 4x2(-5e-5x) + e-5x(2x) = 2xe-5x - 20x2e-5x
    Might wanna check that.
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    (Original post by Zacken)
    Might wanna check that.
    rip

    this is why I'm gonna miss my grades :cry:
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    (Original post by Alexion)
    rip

    this is why I'm gonna miss my grades :cry:
    You'll be more than fine.
 
 
 
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