that means the ones that you can't use like the ones that cause sqare rot of negative or divisinon by 0 so we gots if x=0, then we gots a dvision by 0 if we factored out the x and simplified y=x³-4x
since we factored out the x, thre is a hole at x=0 find the y value y=x³-4x y=0³-4(0) y=0 hole at (0,0) draw an empty circle arount (0,0)
then we have y=x³-4x find roots y=x(x²-4) y=x(x-2)(x+2) roots at x=0,2,-2 wait, 0 is a hole so put the points (2,0) and (-2,0) on the graph then subsitute a bunch of points in y=x³-4x
