\(f(x) = \frac{1}{3}\ctg 15x + \sqrt{3}\) . Найдите \(f'(x)\) .

• \(-\frac{5}{\sin ^2 15x}\)
• \(\frac{5}{\sin ^2 15x}\)
• \(-\frac{1}{3\sin ^2 15x}\)
• \(-\frac{5}{\sin ^2 15x} + \frac{1}{2\sqrt{3}}\)