сos^4(п-x/4)+sin^2(x/4)=1
cos^4(x/4)+sin^2(x/4)=1
(1-sin^2(x/4))^2 +sin^2(x/4)=1
1-2sin^2(x/4)+sin^4(x/4) +sin^2(x/4)=1
sin^4(x/4)-sin^2(x/4)=0
sin^2(x/4)*(sin^2(x/4)-1)=0
sin^2(x/4)=0 sin^2(x/4)=1
sin(x/4)=0 (1-cos(x/2)/2=1
x/4=пk 1-cos(x/2)=2
x=4пk cos(x/2)=-1
x/2=п+2пk
x=2п+2пk
Объединяя эти два решения: x=2пk