cos^4 x+4sin^2 x >=2sin2x cosx
cos^4 x+4sin^2 x-4sinx cos^2 x >=0
(cos^2x-2sinx)^2>=0
cos^2x-2sinx=0
x=2пk,kэ Z
cos^4 x+4sin^2 x >=2sin2x cosx
cos^4 x+4sin^2 x-4sinx cos^2 x >=0
(cos^2x-2sinx)^2>=0
cos^2x-2sinx=0
x=2пk,kэ Z