ctg^4*1x-4ctg^2*2x+3=0
ctg^2*2x=t
t^2-4t+3=0
D=b^2-4ac=16-12=4
t1,2=-b+-корень D/2a
t1=1
t2=3
ctg^2*2x=1
x ={пn/2-п/8; пn/2+п/8}
ctg^2*2x=3
x={пn/2-п/12; пn/2+п/12 }
