Given a polynomial f(x) of fifth degree and g(x) such that
1. a root at 3i
2. a root at 2+4sqrt(3)
3. a root at -1/3
and that f(1)=-7520
Find polynomial f(x) as a product of its factors.
Given the three roots, we can conclude that the two other roots are the conjugates, namely -3i and 2-4sqrt(3).
Since
(x+3i)(x-3i)=x^2+9, and
(x-2+4sqrt(3))(x-2-4sqrt(3)=x^2-4x-44
We conclude that polynomial f(x) has the form
f(x)=a(x^2+9)(x^2-4x-44)(3x+1)
where a is a constant to be determined.
Knowing that f(1)=-7520, we can substitute x=1 in f(x) to get
-7520=a(1^2+9)(1^2-4(1)-44)(3+1)=a(10)(-47)(4)
=>
a=-7520/(-1880)=4
Therefore the polynomial f(x) is defined as
f(x)=4(x^2+9)(x^2-4x-44)(3x+1)
or
f(x)=4(3x+1)(x^2+9)(x^2-4x-44)
