Solve the third-order differential equation using a variation of parameters: y'' + 4y' = sec²(x).
a) y(x) = -¼tan(x) + C₁e⁻⁴ˣ + C₂xe⁻⁴ˣ + C₃x²e⁻⁴ˣ
b) y(x) = ¼tan(x) + C₁e⁻⁴ˣ + C₂xe⁻⁴ˣ + C₃x²e⁻⁴ˣ
c) y(x) = ¼tan(x) + C₁e⁴ˣ + C₂xe⁴ˣ + C₃x²e⁴ˣ
d) y(x) = -¼tan(x) + C₁e⁴ˣ + C₂xe⁴ˣ + C₃x²e⁴ˣ