f（x）=√3cos4x-sin4x=2cos(4x+π/6)函数f（x）最小正周期是π/2x∈[-π/12，π/6]时，4x+π/6∈[-π/6，5π/6]∴当4x+π/6∈[-π/6，0]即x∈[-π/12，-π/24]时f（x）递增4x+π/6∈[0，5π/6]即x∈[-π/24，π/6]时f（x）递减值域[﹣√3,2]
