\(f(x)=\frac{1}{3}ctg15x+\sqrt3.\) Найдите \(f'(x).\)

• \(-\frac{5}{sin^215x}+\frac{1}{2\sqrt3}\)
• \(\frac{5}{sin^215x}\)
• \(-\frac{5}{sin^215x}\)
• \(-\frac{1}{3sin^215x}\)