Polynomial roots of degree 2

Since every polynomial of degree 'n' has 'n' complex roots.

Then what about $P(x)=x^2$ .

Isn't $x=0$ the only possible root of this polynomial ?

Answer

A polynomial of degree $n$ has $n$ roots counting multiplicity. That means that if we have a factor $$(x - a)^k$$

we count the root $a$ a total of $k$ times, once per linear factor. In particular, $x^2$ has a root at $0$ of multiplicity $2$.