Найти производную функции в точке x0=4пи/9 :
y= cos(пи/6 - 3x)

y`=-3*(-sin(π/6-3x)=3sin(π/6-3x)
y`(4π/9)=3sin(π/6-4π/3)=3sin(-7π/6)=-3sin(π+π/6)=-3*(-sinπ/6)=3sinπ/6=
=3*1/2=1,5