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

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