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Mathematics 22 Online
OpenStudy (anonymous):

Given the second order homogenous differential equation

OpenStudy (anonymous):

\[y" +\alpha y'+\beta y =o\] let sum of the root is 94 and the product is 2013. solve the DE

OpenStudy (anonymous):

The characteristic equation you get from the DE is \[r^2+\alpha r+\beta=0\] You know that the sum of the roots to this equation is 94, and that their product is 2013. So, if \(r_1\) and \(r_2\) are roots, then \[\begin{cases} r_1+r_2=94\\ r_1r_2=2013 \end{cases}\] Solving by substitution works nicely: \[\begin{align*}r_2=94-r_1~\Rightarrow~&r_1(94-r_1)=2013\\ &r_1^2-94r_1+2013=0\\ &r_1=33~\text{or}~r_1=61 \end{align*}\] If \(r_1=33\) then \(r_2=61\). Solving for \(\alpha\) and \(\beta\) is pretty simple: just sub these roots for \(r\) and solve the system of equations. From there the solution to the DE is easy to find.

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