Answer:
x=-1,-3,2i and -2i
Step-by-step explanation:
By plugging in x=-1, f(x)=0 and x=-3,f(x)=0
That means x+1 and x+3 are roots of the fourth degree polynomial.
(x+1)(x+3)=x²+4x+3
Divide the polynomial by x²+4x+3 and that gives x²+4.
We now find the zeros of the factors
(x²+4x+3)(x²+4)=0
x=-1,-3,2i and -2i
