Question Number 168575 by qaz last updated on 13/Apr/22
$$\mathrm{Calculate}\:::\:\:\underset{\mathrm{x}\rightarrow+\infty} {\mathrm{lim}}\frac{\left(\mathrm{x}+\mathrm{a}\right)^{\mathrm{x}+\mathrm{a}} \left(\mathrm{x}+\mathrm{b}\right)^{\mathrm{x}+\mathrm{b}} }{\left(\mathrm{x}+\mathrm{a}+\mathrm{b}\right)^{\mathrm{2x}+\mathrm{a}+\mathrm{b}} }=? \\ $$
Answered by LEKOUMA last updated on 14/Apr/22
$$\underset{{x}\rightarrow+\infty} {\mathrm{lim}}\frac{{x}^{{x}+{a}} \left(\mathrm{1}+\frac{{a}}{{x}}\right)^{{x}+{a}} {x}^{{x}+{b}} \left(\mathrm{1}+\frac{{b}}{{x}}\right)^{{x}+{b}} }{{x}^{\mathrm{2}{x}+{a}+{b}} \left(\mathrm{1}+\frac{{a}}{{x}}+\frac{{b}}{{x}}\right)^{\mathrm{2}{x}+{a}+{b}} } \\ $$$$\underset{{x}\rightarrow+\infty} {\mathrm{lim}}\frac{{x}^{\mathrm{2}{x}+{a}+{b}} \left(\mathrm{1}+\frac{{a}}{{x}}\right)^{{x}+{a}} \left(\mathrm{1}+\frac{{b}}{{x}}\right)^{{x}+{b}} }{{x}^{\mathrm{2}{x}+{a}+{b}} \left(\mathrm{1}+\frac{{a}}{{x}}+\frac{{b}}{{x}}\right)^{\mathrm{2}{x}+{a}+{b}} } \\ $$$$\underset{{x}\rightarrow+\infty} {\mathrm{lim}}\frac{\left(\mathrm{1}+\frac{{a}}{{x}}\right)^{{x}+{a}} \left(\mathrm{1}+\frac{{b}}{{x}}\right)^{{x}+{b}} }{\left(\mathrm{1}+\frac{{a}}{{x}}+\frac{{b}}{{x}}\right)^{\mathrm{2}{x}+{a}+{b}} } \\ $$$$\underset{{x}\rightarrow+\infty} {\mathrm{lim}}\frac{{e}^{\left({x}+{a}\right)\:\left(\mathrm{1}+\frac{{a}}{{x}}−\mathrm{1}\right)} {e}^{\left({x}+{b}\right)\left(\mathrm{1}+\frac{{b}}{{x}}−\mathrm{1}\right)} }{{e}^{\left(\mathrm{2}{x}+{a}+{b}\right)\left(\mathrm{1}+\frac{{a}}{{x}}+\frac{{b}}{{x}}−\mathrm{1}\right)} } \\ $$$$\underset{{x}\rightarrow+\infty} {\mathrm{lim}}\frac{{e}^{\left({x}+{a}\right)\left(\frac{{a}}{{x}}\right)} {e}^{\left({x}+{b}\right)\left(\frac{{b}}{{x}}\right)} }{{e}^{\left(\mathrm{2}{x}+{a}+{b}\right)\left(\frac{{a}}{{x}}+\frac{{b}}{{x}}\right)} } \\ $$$$\underset{{x}\rightarrow+\infty} {\mathrm{lim}}\frac{{e}^{{a}+\frac{{a}^{\mathrm{2}} }{{x}}} {e}^{{b}+\frac{{b}^{\mathrm{2}} }{{x}}} }{{e}^{\left(\mathrm{2}+\frac{{a}}{{x}}+\frac{{b}}{{x}}\right)\left({a}+{b}\right)} }=\frac{{e}^{{a}} {e}^{{b}} }{{e}^{\mathrm{2}\left({a}+{b}\right)} }={e}^{{a}+{b}} ×{e}^{−\mathrm{2}\left({a}+{b}\right)} \\ $$$$={e}^{{a}+{b}} ×{e}^{−\mathrm{2}{a}−\mathrm{2}{b}} ={e}^{−{a}−{b}} ={e}^{−\left({a}+{b}\right)} \\ $$