Sin^4x+cos^4x = cos4x

(Sin^2x+cos^2x)^2-2sin^2xcos^2x=1-2sin^2(2x) 1-2sin^2xcos^2x=1-2sin^2x sin^2xcos^2x+sin^2x=0 Sin^2x(cos^2x+1)=0 Cos^2x+1=0 не будет решения Sin^2x=0 Sinx=0 X=pk