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For real constants, the condition $\alpha_1^2 + \alpha_2^2 \neq 0$ is a compact way to state that $\alpha_1$ and $\alpha_2$ are not both zero. This ensures that the boundary condition at the endpoint $x=a$ is nontrivial.

Conditions: The constants $\alpha_1, \alpha_2$ are real numbers.; The boundary condition is $\alpha_1 y(a) + \alpha_2 y'(a) = 0$.

For real constants, the condition $\alpha_1^2 + \alpha_2^2 \neq 0$ is a compact way to state that $\alpha_1$ and $\alpha_2$ are not both zero. This ensures that the boundary condition at the endpoint $x=a$ is nontrivial.

Conditions: The constants $\alpha_1, \alpha_2$ are real numbers.; The boundary condition is $\alpha_1 y(a) + \alpha_2 y'(a) = 0$.

A Sturm-Liouville problem is an eigenvalue problem of the form $L y = \lambda y$ on an interval $a < x < b$, together with homogeneous linear boundary conditions at the endpoints: $\alpha_1 y(a) + \alpha_2 y'(a) = 0$ and $\beta_1 y(b) + \beta_2 y'(b) = 0$. The coefficients at each endpoint cannot both be zero.

Conditions: The equation is posed on an interval $a < x < b$.; Boundary conditions are homogeneous linear combinations of $y$ and $y'$ at $x=a$ and $x=b$.; At each endpoint, the pair of boundary coefficients is not both zero.

A Sturm-Liouville problem is an eigenvalue problem of the form $L y = \lambda y$ on an interval $a < x < b$, together with homogeneous linear boundary conditions at the endpoints: $\alpha_1 y(a) + \alpha_2 y'(a) = 0$ and $\beta_1 y(b) + \beta_2 y'(b) = 0$. The coefficients at each endpoint cannot both be zero.

Conditions: The equation is posed on an interval $a < x < b$.; Boundary conditions are homogeneous linear combinations of $y$ and $y'$ at $x=a$ and $x=b$.; At each endpoint, the pair of boundary coefficients is not both zero.