Hint:
Write in standard form:
Now, use the rational roots theorem to see if this cubic has any integral roots.
Small missing step: If x-a is a factor of a polynomial P(x), then P(a) = 0 (Remainder theorem).
Salahuddin
Maths online
That missing step was given in a duplicate post in another forum. I didn't feel it necessary to repeat it, but rather continued the discussion here after he was asked to post in an appropriate forum.