Cosx-sinx=0
(cos²x/2)-(sin²x/2)-2(sinx/2)(cosx/2)=0 /-cos²x/2≠0
tg²(x/2)+2tg(x/2)-1=0
tgx/2=a
a2+2a-1=0
D=4+4=8
a1=(-2-2√2)=2=-1-√2⇒tgx/2=-1-√2⇒x/2=-arctg(1+√2)+πn⇒x=-2arctg(1+√2)+2πn
a2=(-2+2√2)=2=-1=√2⇒tgx/2=-1+√2⇒x/2=arctg(-1+√2)+πn⇒x=2arctg(-1+√2)+2πn