Question

найдите производную функции f(x)=ln cos^2 4x

Answer 1

$f(x)=ln(cos^24x)\\\\f'(x)=\frac{1}{cos^24x}\cdot (cos^24x)=\frac{1}{cos^24x}\cdot 2\, cos4x\cdot (cos4x)'=\\\\=\frac{1}{cos^24x}\cdot 2\, cos4x\cdot (-sin4x)\cdot (4x)'=-\frac{1}{cos^24x}\cdot 2\, cos4x\cdot sin4x\cdot 4=\\\\=-\frac{8\, sin4x}{cos4x}=-8\, tg4x$