Answer
$${y}=c_{1}+c_{2}\exp^{-5x}$$
Work Step by Step
$$y''+5y=0$$Let $y-e^{\lambda{x}}$ so that $(\ln{y})'=\lambda$.
$${\lambda}^2+5{\lambda}=0$$
$$\lambda(\lambda+5)=0$$
$$\lambda_{1,2}=0,-5$$
$$\therefore{y}=c_{1}+c_{2}\exp^{-5x}$$
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