\(f(x)=\frac{(x-1)(x+2)(x+4)}{(x+1)(x-2)(x-4)}\)
The denominator of a fraction can't be equal to 0.
\((x+1)(x-2)(x-4)
ot= 0 \\
x+1
ot=0 \ \land \ x-2
ot= 0 \ \land \ x-4
ot= 0 \\
x
ot= -1 \ \land \ x
ot = 2 \ \land \ x
ot= 4\)
The function is undefined at x=-1, x=2, x=4, because for these values the denominator of the function would equal 0, and it's impossible to divide by 0.
Edward is correct.