(Cosx+sinx)^2=cos2x
cos^2x +2sinxcosx+sin^2x=cos2x
sin2x+1-cos2x=0
2sinxcosx+sin^2x+cos^2x-cos^2x+sin^2x=0
2sinx(sinx+cosx)=0
sinx=0
x=ПN
sinx=-cosx/ /cosx
tgx=-1
x=-п/4+пN
(Cosx+sinx)^2=cos2x
cos^2x +2sinxcosx+sin^2x=cos2x
sin2x+1-cos2x=0
2sinxcosx+sin^2x+cos^2x-cos^2x+sin^2x=0
2sinx(sinx+cosx)=0
sinx=0
x=ПN
sinx=-cosx/ /cosx
tgx=-1
x=-п/4+пN