Linear Second Order ODE/y'' - 2 y' - 5 y = 0
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Theorem
The second order ODE:
- $(1): \quad y'' - 2 y' - 5 y = 0$
has the general solution:
- $y = C_1 \map \exp {\paren {1 + \sqrt 6} x} + C_2 \map \exp {\paren {1 - \sqrt 6} x}$
Proof
It can be seen that $(1)$ is a constant coefficient homogeneous linear second order ODE.
Its auxiliary equation is:
- $(2): \quad: m^2 - 2 m - 5 = 0$
From Solution to Quadratic Equation with Real Coefficients, the roots of $(2)$ are:
- $m_1 = 1 + \sqrt 6$
- $m_2 = 1 - \sqrt 6$
So from Solution of Constant Coefficient Homogeneous LSOODE, the general solution of $(1)$ is:
- $y = C_1 \map \exp {\paren {1 + \sqrt 6} x} + C_2 \map \exp {\paren {1 - \sqrt 6} x}$
$\blacksquare$