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Second-Order Linear Equations

For constant-coefficient equations, form the characteristic equation and solve for its roots.

$$ay''+by'+cy=0 \quad \Rightarrow \quad ar^2+br+c=0$$

Constant-Coefficient Initial Value

Solve $y''-5y'+6y=0$ if $y(0)=2$ and $y'(0)=5$.

Characteristic equation:

$$r^2-5r+6=0=(r-2)(r-3)$$
$$y=C_1e^{2x}+C_2e^{3x}$$

Apply initial conditions: $C_1+C_2=2$ and $2C_1+3C_2=5$.

Thus $C_1=1$ and $C_2=1$.

Final answer: $y=e^{2x}+e^{3x}$.

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