Найти дифференциал второго порядка y= ln(tg 2x)

[latex]d^2y=y''\,dx^2=\left(\ln\tan 2x\right)''\,dx^2=\left(\dfrac2{\cos^2 2x\tan 2x}\right)'\,dx^2=\\ =\left(\dfrac4{\sin 4x}\right)'\,dx^2=-\dfrac{16\cos 4x}{\sin^24x}\,dx^2[/latex]