Tính d2n biết y= ln9x

\[ - \frac{{9d{x^2}}}{{{x^2}}}\]

\[\frac{{d{x^2}}}{{{x^2}}}\]

\[ - \frac{{d{x^2}}}{{{x^2}}}\]

\[\frac{{9d{x^2}}}{{{x^2}}}\]