Is the following reasoning correct?
According to the complex conjugate root theorem, the number of complex roots of a polynomial is always equal to its degree.
Since odd degree polynomials have a maximum of 2 turning points, they can have a maximum of 3 real roots. And since even degree polynomials have a maximum of 1 turning point, they can have a maximum of 3 real roots.
Therefore, the maximum number of a real roots a polynomial of any degree can have is 3, all other roots are non-real.
Best Answer
I don't know where you got the information that an odd degree polynomial has at most two turning points:
Actually the maximum number of turning points of a degree $n$ polynomial is $n-1$ and the one in the picture indeed has four of them, and five real roots.
Generalizing, if $n$ is any positive integer, the polynomial $$ (x-1)(x-2)\dots(x-n) $$ has $n$ distinct roots.