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differenciation question ...

  • 24-09-2010 1:38am
    #1
    the_monkey
    Closed Accounts Posts: 6,556 ✭✭✭


    y= (x^2.sin(x))/cos(2x)


    I get 2 different answers when i do this the dy/dx = :

    (1) (v.du/dx - u.dv/dx)/v^2


    And when I use the (2) logarithmic method, is it wrong to use the 1st method ?


    Answers
    1. [2x(cos(2x).cos(x) + xsin(2x).sin(x))]/cos^2(2x)


    2. x^2sin(x)/cos(2x)[2/x + cot x + 2tan(2x)]

    They are different answers, as they result in different values when i sub x.



    PS. Sorry for the horrible text, is there a way of getting mathematical notation here ?


Comments

  • #2
    ZorbaTehZ
    Registered Users, Registered Users 2 Posts: 2,149 ✭✭✭ZorbaTehZ


    The problem is with (1) because you are using the quotient rule only, but you need to use the product rule as well because you have x^2.sin(x) in the numerator. There's a few other errors like you forget to keep x^2 in the second part of the quotient rule application in (1).


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