cos(2arctan根號6+三分之派)=?

cos(2arctan根號6+三分之派)=?


令arctan根號6=t
tant=根號6
可求出cos2t,sin2t
cos(2arctan根號6+三分之派)
=cos(2t+pi/3)
=cos2tcos(pi/3)-sin2tsin(pi/3)
下麵就可算出來了



解cos(5x+pai/6)=(根號3)/2


5x+π/6=2kπ±ππ/6
所以5x=2kπ或5x=2kπ-π/3
所以x=2kπ/5或x=2kπ/5-π/15