Linear Second Order ODE/y'' - 4 y = 0/Proof 2

Proof
This is an instance of:
 * Linear Second Order ODE: $y'' - k^2 y = 0$

which yields:
 * $y = C_1 e^{k x} + C_2 e^{-k x}$

where $k = 2$.

Hence the result.