Direction ratios: Difference between points (2, 1, -3) and (0, 0, 0):
\[ (2-0, 1-0, -3-0) = (2, 1, -3). \] Line equation through origin (0, 0, 0) with direction ratios (2, 1, -3): \[ \frac{x-0}{2} = \frac{y-0}{1} = \frac{z-0}{-3} \Rightarrow \frac{x}{2} = \frac{y}{1} = \frac{z}{-3}. \] Answer: \( \frac{x}{2} = \frac{y}{1} = \frac{z}{-3} \).
