решить уравнение f'(x) = 0

1)f(x)=cos^2(x/4)-sin^2(x/4)​

f(x)=cos²(x/4)-sin²(x/4)=cos(2*(x/4))=cos(x/2)

f'(x)=-sin(x/2)*(1/2)=-sin(x/2)/2=0

-sin(x/2)/2=0  |×(-2)

sin(x/2)=0

x/2=πn   |×2

x=2πn.