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Question: Answered & Verified by Expert
$\int_0^2 e^x d x$ Find the value of:
MathematicsIntegrals
Solution:
1280 Upvotes Verified Answer
$\operatorname{Let} \mathrm{I}=\int_0^2 \mathrm{e}^{\mathrm{x}} \mathrm{dx}$ Here, $a=0$ and $b=2$
$$
\begin{aligned}
&\therefore \mathrm{h}=\frac{\mathrm{b}-\mathrm{a}}{\mathrm{n}} \\
&\Rightarrow \mathrm{nh}=2 \text { and } \mathrm{f}(\mathrm{x})=\mathrm{e}^{\mathrm{x}} \\
&\text { Now, } \int_0^2 \mathrm{e}^{\mathrm{x}} \mathrm{dx}=\lim _{\mathrm{h} \rightarrow 0} \mathrm{~h}[\mathrm{f}(0)+\mathrm{f}(0+\mathrm{h})+\mathrm{f}(0+2 \mathrm{~h}) \\
&\quad+\ldots \ldots+\mathrm{f}\{0+(\mathrm{n}-1) \mathrm{h}\}] \\
&\therefore \mathrm{I}=\lim _{\mathrm{h} \rightarrow 0} \mathrm{~h}\left[1+\mathrm{e}^{\mathrm{h}}+\mathrm{e}^{2 \mathrm{~h}}+\ldots+\mathrm{e}^{(\mathrm{n}-1)} \mathrm{h}\right] \\
&=\lim _{\mathrm{h} \rightarrow 0} \mathrm{~h}\left[\frac{1 \cdot\left(\mathrm{e}^{\mathrm{h}}\right)^{\mathrm{n}}-1}{\mathrm{e}^{\mathrm{h}}-1}\right]=\lim _{\mathrm{h} \rightarrow 0} \mathrm{~h}\left(\frac{\mathrm{e}^{\mathrm{nh}}-1}{\mathrm{e}^{\mathrm{h}}-1}\right) \\
&=\lim _{\mathrm{h} \rightarrow 0} \mathrm{~h}\left(\frac{\mathrm{e}^2-1}{\mathrm{e}^{\mathrm{h}}-1}\right) \\
&=\mathrm{e}^2 \lim _{\mathrm{h} \rightarrow 0} \frac{\mathrm{h}}{\mathrm{e}^{\mathrm{h}}-1}-\lim _{\mathrm{h} \rightarrow 0} \frac{\mathrm{h}}{\mathrm{e}^{\mathrm{h}}-1}\left[\because \lim _{\mathrm{h} \rightarrow 0} \frac{\mathrm{h}}{\mathrm{e}^{\mathrm{h}}-1}=1\right]
\end{aligned}
$$
$$
=\mathrm{e}^2-1
$$
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