Question Number 66245 by aliesam last updated on 11/Aug/19
![prove that ∫e^x dx = e^x + c](https://www.tinkutara.com/question/Q66245.png)
$${prove}\:{that} \\ $$$$ \\ $$$$\int{e}^{{x}} \:{dx}\:=\:{e}^{{x}} \:+\:{c} \\ $$
Commented by Rio Michael last updated on 11/Aug/19
![let y = e^x (dy/dx) = e^x ∫(dy/dx) = ∫e^x dx ⇒ y = e^x + c](https://www.tinkutara.com/question/Q66251.png)
$${let}\:\:{y}\:=\:{e}^{{x}} \\ $$$$\:\:\:\:\:\frac{{dy}}{{dx}}\:=\:{e}^{{x}} \\ $$$$\int\frac{{dy}}{{dx}}\:=\:\int{e}^{{x}} {dx} \\ $$$$\:\Rightarrow\:{y}\:=\:{e}^{{x}} \:+\:{c} \\ $$
Commented by mathmax by abdo last updated on 11/Aug/19
![∫ e^x dx =∫ (Σ_(n=0) ^∞ (x^n /(n!)))dx =Σ_(n=0) ^∞ (1/(n!))∫ x^n dx =Σ_(n=0) ^∞ (1/(n!))(1/(n+1))x^(n+1) +c =Σ_(n=0) ^∞ (x^(n+1) /((n+1)!)) +c =Σ_(n=1) ^∞ (x^n /(n!)) +c =Σ_(n=0) ^∞ (x^n /(n!)) +c−1 =e^x +C (C=c−1)](https://www.tinkutara.com/question/Q66254.png)
$$\int\:{e}^{{x}} {dx}\:=\int\:\left(\sum_{{n}=\mathrm{0}} ^{\infty} \:\frac{{x}^{{n}} }{{n}!}\right){dx}\:=\sum_{{n}=\mathrm{0}} ^{\infty} \:\frac{\mathrm{1}}{{n}!}\int\:{x}^{{n}} {dx} \\ $$$$=\sum_{{n}=\mathrm{0}} ^{\infty} \:\frac{\mathrm{1}}{{n}!}\frac{\mathrm{1}}{{n}+\mathrm{1}}{x}^{{n}+\mathrm{1}} \:+{c}\:=\sum_{{n}=\mathrm{0}} ^{\infty} \:\:\frac{{x}^{{n}+\mathrm{1}} }{\left({n}+\mathrm{1}\right)!}\:+{c} \\ $$$$=\sum_{{n}=\mathrm{1}} ^{\infty} \:\frac{{x}^{{n}} }{{n}!}\:+{c}\:=\sum_{{n}=\mathrm{0}} ^{\infty} \:\frac{{x}^{{n}} }{{n}!}\:+{c}−\mathrm{1}\:={e}^{{x}} \:+{C}\:\:\:\:\:\:\left({C}={c}−\mathrm{1}\right) \\ $$
Answered by mr W last updated on 12/Aug/19
![since ((d(e^x +c))/dx)=((d(e^x ))/dx)+((d(c))/dx)=e^x +0=e^x ⇒∫e^x dx=e^x +c](https://www.tinkutara.com/question/Q66299.png)
$${since}\:\frac{{d}\left({e}^{{x}} +{c}\right)}{{dx}}=\frac{{d}\left({e}^{{x}} \right)}{{dx}}+\frac{{d}\left({c}\right)}{{dx}}={e}^{{x}} +\mathrm{0}={e}^{{x}} \\ $$$$\Rightarrow\int{e}^{{x}} {dx}={e}^{{x}} +{c} \\ $$