Theoretical Ordinary Differential Equation with the lim Yg = 0












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I was given a theoretical problem in my Linear Algebra and Differentials class and I am stumped on how to approach this problem.



Consider the ODE y''+ay'+by=0 where a and b are constants such that $a^2$ < 4b. What conditions on a and b guarentees that the general solution of the ODE satisfies $displaystyle{lim_{x to infty} Yg=0}$



So I do understand that Yg is the general solution, which contains the homogeneous solution + the particular solution.



So far we have worked with simple polynomials in our class, so what we do is we solve for the particular solution first and use $y=C1e^(r1*x) + C2e^(r2*x)$ where t1 and t2 are the roots to the equation $r^2+ar+b=0$ (from above equation).



The way we solve the particular solution is by "Guessing" the right hand side of this equation, but since it is = 0 I believe that the Yg is just the Y homogeneous.



$Yg = Yh+Yp => Yg = Yh+0 => Yg=Yh$



So in this case I believe my Yg would be of the form $Yg = e^(r1*x) + e^(r2*x)$ which implies that my lim equation is $displaystyle{lim_{x to infty} e^(r1*x) + e^(r2*x)=0}$



I am not sure if this is right at all, but this is how I would currently approach it. I just have no idea how to satisfy the constraint given of $a^2<4b$ and that the limit of Yg is = 0.



Any guidance would be greatly appreciated.










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    $begingroup$


    I was given a theoretical problem in my Linear Algebra and Differentials class and I am stumped on how to approach this problem.



    Consider the ODE y''+ay'+by=0 where a and b are constants such that $a^2$ < 4b. What conditions on a and b guarentees that the general solution of the ODE satisfies $displaystyle{lim_{x to infty} Yg=0}$



    So I do understand that Yg is the general solution, which contains the homogeneous solution + the particular solution.



    So far we have worked with simple polynomials in our class, so what we do is we solve for the particular solution first and use $y=C1e^(r1*x) + C2e^(r2*x)$ where t1 and t2 are the roots to the equation $r^2+ar+b=0$ (from above equation).



    The way we solve the particular solution is by "Guessing" the right hand side of this equation, but since it is = 0 I believe that the Yg is just the Y homogeneous.



    $Yg = Yh+Yp => Yg = Yh+0 => Yg=Yh$



    So in this case I believe my Yg would be of the form $Yg = e^(r1*x) + e^(r2*x)$ which implies that my lim equation is $displaystyle{lim_{x to infty} e^(r1*x) + e^(r2*x)=0}$



    I am not sure if this is right at all, but this is how I would currently approach it. I just have no idea how to satisfy the constraint given of $a^2<4b$ and that the limit of Yg is = 0.



    Any guidance would be greatly appreciated.










    share|cite|improve this question









    $endgroup$















      0












      0








      0





      $begingroup$


      I was given a theoretical problem in my Linear Algebra and Differentials class and I am stumped on how to approach this problem.



      Consider the ODE y''+ay'+by=0 where a and b are constants such that $a^2$ < 4b. What conditions on a and b guarentees that the general solution of the ODE satisfies $displaystyle{lim_{x to infty} Yg=0}$



      So I do understand that Yg is the general solution, which contains the homogeneous solution + the particular solution.



      So far we have worked with simple polynomials in our class, so what we do is we solve for the particular solution first and use $y=C1e^(r1*x) + C2e^(r2*x)$ where t1 and t2 are the roots to the equation $r^2+ar+b=0$ (from above equation).



      The way we solve the particular solution is by "Guessing" the right hand side of this equation, but since it is = 0 I believe that the Yg is just the Y homogeneous.



      $Yg = Yh+Yp => Yg = Yh+0 => Yg=Yh$



      So in this case I believe my Yg would be of the form $Yg = e^(r1*x) + e^(r2*x)$ which implies that my lim equation is $displaystyle{lim_{x to infty} e^(r1*x) + e^(r2*x)=0}$



      I am not sure if this is right at all, but this is how I would currently approach it. I just have no idea how to satisfy the constraint given of $a^2<4b$ and that the limit of Yg is = 0.



      Any guidance would be greatly appreciated.










      share|cite|improve this question









      $endgroup$




      I was given a theoretical problem in my Linear Algebra and Differentials class and I am stumped on how to approach this problem.



      Consider the ODE y''+ay'+by=0 where a and b are constants such that $a^2$ < 4b. What conditions on a and b guarentees that the general solution of the ODE satisfies $displaystyle{lim_{x to infty} Yg=0}$



      So I do understand that Yg is the general solution, which contains the homogeneous solution + the particular solution.



      So far we have worked with simple polynomials in our class, so what we do is we solve for the particular solution first and use $y=C1e^(r1*x) + C2e^(r2*x)$ where t1 and t2 are the roots to the equation $r^2+ar+b=0$ (from above equation).



      The way we solve the particular solution is by "Guessing" the right hand side of this equation, but since it is = 0 I believe that the Yg is just the Y homogeneous.



      $Yg = Yh+Yp => Yg = Yh+0 => Yg=Yh$



      So in this case I believe my Yg would be of the form $Yg = e^(r1*x) + e^(r2*x)$ which implies that my lim equation is $displaystyle{lim_{x to infty} e^(r1*x) + e^(r2*x)=0}$



      I am not sure if this is right at all, but this is how I would currently approach it. I just have no idea how to satisfy the constraint given of $a^2<4b$ and that the limit of Yg is = 0.



      Any guidance would be greatly appreciated.







      ordinary-differential-equations limits






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      asked Dec 18 '18 at 23:24









      97WaterPolo97WaterPolo

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