Question

Find all possible rational zeros: x^3-x^2+4x+3

Answer 1

So far I did:
3/1 = 3
Possible zeros: + or - 1, + or - 3
But the book says that 5 and 15 are also possible zeros and I don't get that

Answer 2

but those are not rational zeros are they? f(-1) and f(3) has remainders

Answer 3

I don't think they have to be the actual zeros, just the list of the possible zeros. The question wants me to do the Rational Zeros Theorem.