Решить 1. 4ctg^4(x)-5ctg^2(x)+1=0 2. cos2x/1+ctgx=0 3. 7sin^2(5x)-4sin(10x)+cos^2(5x)=0 4. (cos2x+sin2x)^2=cos(4x-pi)

1. ctg^2(x)=t>=0; 4t^2-5t+1=0; t1=1; ctg^2(x)=1; ctg(x)=+ -1; x=+-pi/4 +pik t2=1/4; ctg^2(x)=1/4; ctg(x)= - 1/2; x= pi-acrctg(1/2)+pik; ctg(x)1/2; x=arcctg(1/2)+pik