cos(x) has a maximum at x=0
It is also a periodic function with a period of 2pi.So, the values of x for which cos(x) is maximum is x =0, 2Pi, 4π, 6π , .....
and -2π, -4π, -6π , .....
So, The formula gives the x-coordinates of the maximum values for y = cos(x)
[tex]k \pi \ for \ k \ =0 , \pm 2, \pm4 [/tex]
