If x^2 - 9 = 0 and x > 0, which of…

If x^2 - 9 = 0 and x > 0, which of the following must be equal to 0 ?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #9293