Решите уравнение
cos^4 (2x) - cos^2 (4x) = 0

(1+cos4x)²/4-cos²4x=01+2cos4x+cos²4x-4cos²4x=03cos²4x-2cos4x-1=0cos4x=a3a²-2a-1=0D=4+12=16a1=(2-4)/6=-1/3⇒cos4x=-1/3⇒4x=+-(π-arccos1/3)+2πn⇒x=+-1/4(π-arccos1/3)+πn/2a2=(2+4)/6=1⇒cos4x=1⇒4x=2πn⇒x=πn/2