Recall that if a polynomial equation can be factored into the form
0= (x-a)(x-b)(x-c), the intercepts will be at the x values of a, b and c.
You have been asked to do the reverse. Given intercepts of -1, 2 and 3, let a= -1, let b=2 and let c=3.
Plug into the above equation to get
Note that for three x intercepts, the minimum degree of the polynomial will be 3. There are no extra or duplicated roots in the above.
Multiply this out to get the final answer
f(x)= x^3 - 4x^2 + x + 6