cos x cos П/4 - sin x sin П/4=1

формула: cos(a+b)=cosa*cosb - sin a*sinbcosx*cos π/4 -sinx*sin π/4=1cos(x+π/4)=1x+π/4=±arccos1+2πn, n € Zx+π/4=π/2+πn, n€Zx=π/2-π/4+πn, n € Zx=π/4+πn, n € Z -ответ