.
Since the leading coefficient is 1, the Remainder theorem provides this list of possible zeros
(all of them are divisors of the constant term 45, in this case)
+/-1, +/-3, +/-5, +/-9, +/-15, +/-45.
Next, the plot below
Plot y =
shows the root x= 3 of the multiplicity at least 2.
So, I divide by , and I get the quotient .
This quotient is a quadratic polynomial with negative discriminant, so it has no real roots.
Therefore, factoring over real numbers is
= .
You may go forward to find complex zeroes of the quadratic quotient.