обчислiть а)ctg 630°
б)cos 15Пи/4

ctg630°=ctg(540°+90°)=ctg90°=0cos(15π/4)=cos(16π/4 - π/4)=cos(4π-π/4)=cos(-π/4)=cos(π/4)=(√2)/2ctg (x+kπ)=ctgxcos(x+2kπ)=cosxcos(-x)=cosx