1) cos^4x=cos2x
2) 2sin^2x+cos4x=0

ответ. (sin(x))^4+(cos(x))^4=(cos(2*x))^2+1/4; (sin(x))^4+(cos(x))^4=((cos(x))^2-(sin(x))^2)^2+1/4; 0=-2*(cos(x))^2*(sin(x))^2+1/4; -0,5*(sin(2*x))^2+0,25=0; (sin(2*x))^2=0,5; sin(2*x1)=(0,5)^0,5; sin(2*x2)=-(0,5)^0,5;