Correct answer: [0, π/2)
The function f(x) is defined where each component is valid: 4^(-x²) is defined for all x, cos⁻¹((x/2) - 1) requires (x/2) - 1 to be in [0, 1], which restricts x to [0, 2], and log(cos x) is defined where cos x > 0, limiting x to (−π/2, π/2). The intersection of these conditions gives the interval [0, π/2).