Giải thích các bước giải:
\(\begin{array}{l}
\frac{3}{{{x^2} + 6x + 9}} + \frac{5}{{{x^2} - 9}}\\
= \frac{3}{{{{(x + 3)}^2}}} + \frac{5}{{(x - 3)(x + 3)}}\\
= \frac{{3(x - 3)}}{{{{(x + 3)}^2}(x - 3)}} + \frac{{5(x + 3)}}{{(x - 3){{(x + 3)}^2}}}\\
= \frac{{3x - 9 + 5x + 15}}{{{{(x + 3)}^2}(x - 3)}} = \frac{{8x - 6}}{{{{(x + 3)}^2}(x - 3)}}
\end{array}\)
