[Math] Is every real root also a complex root? (Complex zeros and Fundamental Theorem of Algebra)

algebra-precalculus

Stupid question about this topic: I don't understand the rule that says "A poly with degree N will have N complex roots". eg: $P(X)=x^5 + x^3 – 1$ is a 5th degree polynomial function, so P(x) has exactly 5 complex zeros. Sorry, but how do you know it will have 5 complex zeros? Maybe it factors into only real/integer roots? Or, is every real root also a complex root? ie: $x = x + 0i$

What is a complex polynomial function (which has at least one complex zero)? Just a poly with an "i" in the coefficient? eg: $4ix^2 + …$

Disclaimer: I am not a student trying to get free internet homework help. I am an adult who is learning Calculus from a textbook. I am deeply grateful to the members of this community for their time.

Best Answer

Yes, real numbers are complex numbers with imaginary part $0$.