Differential Equations

The complementary function of $\frac{d^2 y}{dx^2} + 4y = 0$ is:

Options:

• (A) $C_1 \cos(2x) + C_2 \sin(2x)$
• (B) $C_1 e^{2x} + C_2 e^{-2x}$
• (C) $(C_1 + C_2 x) e^{2x}$
• (D) $C_1 \cos(4x) + C_2 \sin(4x)$