[m]=\lim_{x \to\infty }(\frac{x+1}{x+3})^{4x}\cdot\lim_{x \to\infty }(\frac{x+1}{x+3})^{-1}=[/m]
[m]\lim_{x \to\infty }(\frac{x+1}{x+3})^{-1}= 1^{-1}=1[/m]
[m]\lim_{x \to\infty }(\frac{x+1}{x+3})^{4x}=\lim_{x \to\infty }(\frac{\frac{x+1}{x}}{\frac{x+3}{x}})^{4x}=[/m]
[m]=\lim_{x \to\infty }\frac{(1+\frac{1}{x})^{x})^{4}}{(1+\frac{3}{x})^{x})^{4}}=\frac{e^{4}}{(e^{3})^{4}}=e^{4-12}=e^{-8}[/m]