sin810 * cos900 + tg585 ctg1845 + cos135 sin405 =
=sin(720 + 90) * cos(720 + 180) + tg(-135) * ctg(45)+
+ cos(90 + 45) * sin(360 + 45) = sin90 * cos180 + tg(45) * ctg(45) - sin45 * sin45 = 1 * (-1) + 1 * 1 -1/2 = -1/2
