NOTE: <= (less than or equal to)
any help much appreciated!
What are the values of x when this values are satisfied
For x= 0 This happens when x= 90degree or x = - 90 degrees
And for cos(x)= -1 this happens when x= 180degree or x= -180 degree
This is done using the property that
ie; if the answer is 90 degree than answer is also -90 degree as this value also lies in the domain