2 cos (3t-П/4)=1/2
cos (3t-П/4)=1/4
3t-П/4= ±аrccos(1/4)+ 2Пn, n є z
3t= ±аrccos(1/4)+П/4 + 2Пn, n є z
t= ±(аrccos(1/4))/3+П/12 + 2Пn/3, n є z
