1. The problem statement, all variables and given/known data I have the metric ##ds^2 = -X^2dT^2 + dX^2## Find the coordinate transformation that reduces the metric to that of flat spacetime: ##ds^2 = -dt^2 + dx^2## 2. Relevant equations 3. The attempt at a solution I'm not sure there's a systematic way to solve this (or in general to show that a metric is just flat spacetime in a different coordinate system). And I've not been able to guess a suitable transformation. Any advice or hints on a technique or an inspired guess?