f(x)=x^3-3x^2-x+3

=x^2(x-3)-(x-3)

=(x-3)(x^2- 1)

=(x-3)(x+ 1)(x- 1)

Zero, that is, f(x)=0.

Then x=- 1, 1, 3. The zeros are-1, 1 and 3.