Question

Find any values of x that must be excluded from the domain. This part really confuses me.

Answer 1

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

Answer 2

The only restriction on the domain is that division by zero is undefined, or "not allowed", so x cannot equal zero.

So the domain is x=(-oo,0),(0,+oo)