a) \(\frac{-3}{x+4}-\frac{5}{x-4}=0\) \(\left(ĐKXĐ:x\ne\pm4\right)\)
\(\Leftrightarrow-3\left(x-4\right)-5\left(x+4\right)=0\)
\(\Leftrightarrow-3x+12-5x-20=0\)
\(\Leftrightarrow-8x-8=0\)
\(\Leftrightarrow x=-1\)
b) \(\frac{7}{x+2}+\frac{2}{x+3}=\frac{1}{x^2+5x+6}\) \(\left(ĐKXĐ:x\ne-2;x\ne-3\right)\)
\(\Leftrightarrow7\left(x+3\right)+2\left(x+2\right)=1\)
\(\Leftrightarrow7x+21+2x+4=1\)
\(\Leftrightarrow x=-\frac{8}{3}\)