More polynomial .... help please?

Question

I have started this problem and am stuck ... this is what I have so far ...

Zeros: -3, 0, 4; degree 3

f(x)=(x+3)(x-0)(x-4)
=(x^2+3)(x-4)
=x^3-12+3x-4x^2

the answer is supposed to be:
f(x)=x^3 - x^2 - 12x for a = 1

Answer 1

You did your multiplication wrong. At the second line you should have (x^2-3x)* (x-4). Try that out.

Answer 2

f(x)=(x+3)(x-0)(x-4)
=(x^2+3x)(x-4) [you forgot the x after the 3]
=x^3-12x+3x^2-4x^2
=x^3-x^2-12x