Question

A discriminant of 0 indicates what type of roots?

Answer 1

Ummm, I suppose it means that you only have 1 root, and it's a real root.
Example:\[\large 0=x^2-2x+1\]Throwing this into the Quadratic Formula gives us,\[\large x=\frac{2 \pm \sqrt{2^2-4(1)(1)}}{2} \qquad \rightarrow \qquad x=1\]

Answer 2

One Rational Double

Answer 3

Yes, that sounds right :)
It's a repeated, or "double", root since there is only one.