Обчислiть а)ctg 630°б)cos 15Пи/4

Question

Обчислiть а)ctg 630°
б)cos 15Пи/4

Answer 1

Ctg630°=ctg(540°+90°)=ctg90°=0

cos(15π/4)=cos(16π/4 - π/4)=cos(4π-π/4)=cos(-π/4)=cos(π/4)=(√2)/2


ctg (x+kπ)=ctgx
cos(x+2kπ)=cosx
cos(-x)=cosx