tg^2x=(1-sin x) (1-cos x) tg^2x=1-sin^2x

tg^2x=(1-sin x) (1-cos x) tg^2x=1-sin^2xtg^2x=cos^2xsin^2x/cos^2x=cos^2xsin^2x=cos^4x1-cos^2x=cos^4xcos^2x=t0 <= t <= 11-t=t^2t^2+t-1=0D=1+4=5t1=(-1+sqrt 5) /2t2=(-1-sqrt 5) /2<-1cos^2x=(-1+sqrt 5) /2cosx=+- (sqrt (5) -1) /2x=+-arccos[+- (sqrt (5) -1) /2]+2πn, n є Z