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Math Help - Second Derivative of Trigonometry function

  1. #1
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    Second Derivative of Trigonometry function

    Dear All,

    I'm a newbie here and wish to seek assistance from expert here.

    I have one question in the past year exam question. the question is

    (4y^3)*(d^2y/dx^2)+(y^4)+1=0

    where y=(cos x)^1/2

    i really seek assistance from experts here..

    thank you,
    Last edited by mr fantastic; November 30th 2011 at 01:30 AM. Reason: Deleted email address.
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  2. #2
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    Re: Second Derivative of Trigonometry function

    Quote Originally Posted by wa1515 View Post
    Dear All,

    I'm a newbie here and wish to seek assistance from expert here.

    I have one question in the past year exam question. the question is

    (4y^3)*(d^2y/dx^2)+(y^4)+1=0

    where y=(cos x)^1/2

    i really seek assistance from experts here..

    thank you,
    y'_x=\frac{1}{2\sqrt{\cos x}}\cdot (-\sin x)=\frac{-\sin x}{2\sqrt{\cos x}}

    y''_x=\frac{(-\sin x)'_x\cdot 2\sqrt{\cos x}-(-\sin x)\cdot(2\sqrt{\cos x})'_x}{4\cos x}
    Last edited by mr fantastic; November 30th 2011 at 01:30 AM.
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  3. #3
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    Re: Second Derivative of Trigonometry function

    Quote Originally Posted by wa1515 View Post
    Dear All,

    I'm a newbie here and wish to seek assistance from expert here.

    I have one question in the past year exam question. the question is

    (4y^3)*(d^2y/dx^2)+(y^4)+1=0

    where y=(cos x)^1/2

    i really seek assistance from experts here..

    thank you,
    It would help if you posted the actual question. Are we to assume that the actual question asks you to verify y=(cos x)^1/2 as a solution to the DE and your problem is in calculating d^2y/dx^2?
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