I have a question about a/the in mathematics.
I would like to say that x=1 is a/the root of the polynomial (x-1)(x-2).
There are two roots of this polynomial, that is, x=1,2. So x=1 is "a" root of the polynomial? Or should it be "the"?
As J.R. mentions in his comment, if there is more than one something in a list you can either say "a [something]" or "one of the [somethings]"
Goodfellas is a Martin Scorsese film.
Goodfellas is one of Martin Scorsese's films.
So "1" is either "a root" or "one of the roots" of the equation.
Use "the" when there is only one root. Use "a" when there is more than one root, or you don't know the exact number of roots.