Calcolare la derivata della funzione
[math]f(x) = \frac{-1}{2 \\sin^2 x} + \\log \\ an x[/math]
[math]f'(x) = \frac{4 \\sin x \\cos x}{4 \\sin^4 x} + \frac{1}{\\ an x} \cdot \frac{1}{\\cos^2 x} =[/math]
[math]\frac{1}{\\ an x} \cdot ( \frac{1}{\\sin^2 x} + \frac{1}{\\cos^2 x} ) =[/math]
[math]\frac{\\cos x}{\\sin x} \cdot \frac{1}{\\sin^2 x \cdot \\cos^2 x} = \frac{1}{\\sin^3 x \\cos x}[/math]