To get the restriction you need to find the values for x for which:

-4x+1=0 an 4x + 1 = 0

By solving -4x+1=0 we find x = 1/4.

By solving 4x + 1 = 0 we find x = -1/4.

So the restrictions are: the solution x can not be -1/4 nor 1/4.