1)cosx = 0,1
x = +-arccos0,1 + 2pin, n=Z
2)cos5x = 1
5x = 2pin
x = 2pin/5, n=Z
3)2cos3x = -1
cos3x = -1/2
3x = +-arccos -1/2 + 2pin
3x = +-2pi/3 + 2pin
x = +-2pi/9 + 2pin/3, n=Z
1)cosx = 0,1
x = +-arccos0,1 + 2pin, n=Z
2)cos5x = 1
5x = 2pin
x = 2pin/5, n=Z
3)2cos3x = -1
cos3x = -1/2
3x = +-arccos -1/2 + 2pin
3x = +-2pi/3 + 2pin
x = +-2pi/9 + 2pin/3, n=Z