How can you tell whether a solution of a polynomial equation is a repeated solution when the equation is written in factored form

Example:-

(x + 1) ^2 (x - 1)

will have a root - 1 duplicity 2 because the (x + 1) is squared

(x - 1) ^3 (x + 9) ^2

- will have 5 roots: - 1 with duplicity 3 and - 9 with duplicity 2