Practicing Success
The value of $\underset{x→0}{\lim}\frac{(1+x)^{1/x}-e+\frac{ex}{2}}{x^2}$ is |
$\frac{11e}{24}$ $-\frac{11e}{24}$ $\frac{e}{24}$ none of these |
$\frac{11e}{24}$ |
$\underset{x→0}{\lim}\frac{(1+x)^{1/x}-e+\frac{ex}{2}}{x^2}$ $(1+x)^{1/x}$ can be expanded as $y=(1+x)^{1/x}$ $\log y=\frac{1}{x}\log (1+x)=\frac{1}{x}\left[x-\frac{x^2}{2}+\frac{x^3}{3}\right]$ [Higher power is neglected as → 0] $⇒y=e^{1-\frac{x}{2}+\frac{x^2}{3}}=e[e^{-\frac{x}{2}+\frac{x^2}{3}}]$ Now from the expansion of exponential function $y=e\left[1+\left(\frac{-x}{2}+\frac{x^2}{3}\right)+\frac{1}{2!}\left[\frac{x^2}{4}+\frac{x^4}{9}-\frac{2x^3}{6}\right]+......\right]$ Thus, $y=e-\frac{ex}{2}+ex^2[\frac{1}{3}+\frac{1}{8}]$+ higher powers Therefore, $\underset{x→0}{\lim}\frac{(1+x)^{1/x}-e+\frac{ex}{2}}{x^2}=\underset{x→0}{\lim}\frac{e-\frac{ex}{2}+x^2(\frac{11}{24})e-e+\frac{ex}{2}}{x^2}=\frac{11e}{24}$ |