In order to find the polynomials that have these roots, we can use the factored form of a polynomial with 4 roots:
So the polynomials that have the roots -1, -2, 3 and 7 are:
Since a can be any real value, so there is an infinite number of polynomials with these roots.
If the polynomial has 4 roots, it is a 4th-degree polynomial.
Since (x-7) is a factor of P(x), we can write P(x) = (x-7)Q(x).
The degree of Q(x) is 3, since one of the roots was "removed" from P(x).
Since (x+8) is not a factor of P(x), we can't write P(x) = (x+8)Q(x).