1. cosx = - sqrt(2)/2
sinx = sqrt(1 - cos^2x) = sqrt(1 - 2/4) = sqrt(2)/2
tgx = sinx/cosx = 1
ctgx = 1
2. 1-cos^2x/sinx = sin^2x/sinx = sinx
3. ctgx*tgx+tg^2x = 1/cos^2x
ctgx*tgx+tg^2x = 1 + tg^2x = 1/cos^2x
1/cos^2x = 1/cos^2x
4. sinx = 1/2
x = (-1)^n arcsin 1/2 + pin, n є Z
x=(-1)^n pi/6 + pin, n є Z