The given Trigonometric function is
y = Cos (x)
As the maximum value of Cosine (Theta) is 1. i.e
Maximum value of Cos (x) = 1
Cos (x) = cos (0 or 2 π)
If Cos (x) = Cos A
Then General formula for evaluating x is ,
x = 2 n π A, for n =......-3,-2,-1,0,1,2,3,4,5.....
Here, A= 0, so the value of x is =2 n π 0
x= 2 n π