a.
ĐKXĐ:...
\(=\dfrac{x^3+3x^2+2x-3x^2-9x-6}{\left(x-3\right)^2\left(x^2+4x+4\right)}=\dfrac{x\left(x^2+3x+2\right)-3\left(x^2+3x+2\right)}{\left(x-3\right)^2\left(x+2\right)^2}\)
\(=\dfrac{\left(x-3\right)\left(x^2+3x+2\right)}{\left(x-3\right)\left(x+2\right)^2}=\dfrac{\left(x-3\right)\left(x+1\right)\left(x+2\right)}{\left(x-3\right)^2\left(x+2\right)^2}\)
\(=\dfrac{x+1}{\left(x-3\right)\left(x+2\right)}\)
b.
\(\dfrac{35.\left(\left(3^3\right)^8+2.\left(3^2\right)^{11}\right)}{15\left(\left(3^4\right)^6-4.3.3^{19}\right)}=\dfrac{35\left(3^{24}+2.3^{22}\right)}{15.\left(3^{24}-4.3^{20}\right)}\)
\(=\dfrac{7.5.3^{22}.\left(3^2+2\right)}{3.5.3^{20}.\left(3^4-4\right)}=\dfrac{7.3.11}{5.77}=\dfrac{77.3}{5.77}=\dfrac{3}{5}\)