Well, I guess the first question is, "what do you think a 'critical point' is?" What definition are you using? What points do you think would be critical points?
I suspected that. First, a value of x is NOT a critical point. A critical point is a point, (x,y), on the graph of the function, such that the derivative is 0 or does not exist. Here, x= 1 or x= -1 does not give a critical point because there is no point on the graph of y= f(x) which x= 1 or x= -1.