=ctg 1*sin 1-cos 1=cos 1/sin 1*sin 1-cos 1=cos 1-cos 1=0
формулы приведения: tg((3π/2)-x) = ctg(x)
sin(π-x) = sin(x) и cos(π+x) = -cos(x)
х3 + 2х2 – 5х – 6 = 0