Question Number 6441 by Temp last updated on 27/Jun/16
$$\mathrm{After}\:\mathrm{looking}\:\mathrm{at}\:\mathrm{a}\:\mathrm{previous}\:\mathrm{question} \\ $$$$\mathrm{I}\:\mathrm{was}\:\mathrm{wondering}\:\mathrm{if}\:\mathrm{the}\:\mathrm{following} \\ $$$$\mathrm{is}\:\mathrm{correct}: \\ $$$${I}\left({n}\right)=\int_{\mathrm{0}} ^{\:{n}} \left(−\mathrm{1}\right)^{{x}} {dx},\:\:{n}\in\mathbb{R} \\ $$$${I}\left({n}\right)=\int_{\mathrm{0}} ^{\:{n}} {e}^{{i}\pi{x}} {dx}\:\:\:\left(\mathrm{1}\right) \\ $$$${I}\left({n}\right)=−\frac{{i}}{\pi}\left({e}^{{i}\pi{x}} \right)_{\mathrm{0}} ^{{n}} \\ $$$${I}\left({n}\right)=−\frac{{i}}{\pi}\left({e}^{{i}\pi{x}} \right)_{\mathrm{0}} ^{{n}} \\ $$$${I}\left({n}\right)=−\frac{{i}}{\pi}\left({e}^{{i}\pi{n}} −\mathrm{1}\right) \\ $$$$ \\ $$$${I}\left({n}\right)=\int_{\mathrm{0}} ^{\:{n}} \left(\mathrm{cos}\left({x}\right)+{i}\mathrm{sin}\left({x}\right)\right){dx}\:\:\:\left(\mathrm{2}\right) \\ $$$${I}\left({n}\right)=\left(\mathrm{sin}\left({x}\right)−{i}\mathrm{cos}\left({x}\right)\right)_{\mathrm{0}} ^{{n}} \\ $$$${I}\left({n}\right)=−{i}\left(\mathrm{cos}\left({x}\right)+{i}\mathrm{sin}\left({x}\right)\right)_{\mathrm{0}} ^{{n}} \\ $$$${I}\left({n}\right)=−{i}\left({e}^{{i}\pi{n}} −\mathrm{1}\right) \\ $$$$ \\ $$$$\mathrm{Which}\:\mathrm{is}\:\mathrm{correct}? \\ $$
Commented by Yozzii last updated on 27/Jun/16
$${In}\:\left(\mathrm{2}\right)\:{cosx}+{isinx}={e}^{{ix}} \neq{e}^{\pi{ix}} . \\ $$$$\int_{\mathrm{0}} ^{{n}} {e}^{{ix}} {dx}=\frac{\mathrm{1}}{{i}}{e}^{{ix}} \mid_{\mathrm{0}} ^{{n}} =−{i}\left({e}^{{ni}} −\mathrm{1}\right) \\ $$$$\left(\mathrm{1}\right)\:{is}\:{correct},\:\left(\mathrm{2}\right)\:{is}\:{incorrect}. \\ $$
Commented by Temp last updated on 27/Jun/16
$$\mathrm{A}{hhh},\:\mathrm{thanks}!\:\mathrm{Silly}\:\mathrm{error} \\ $$
Commented by Temp last updated on 27/Jun/16
$$\mathrm{I}\:\mathrm{checked}\:\mathrm{and}\:\mathrm{if}\:\mathrm{i}\:\mathrm{fix}\:\left(\mathrm{2}\right)\:\mathrm{it}\:\mathrm{has}\:\mathrm{the} \\ $$$$\mathrm{same}\:\mathrm{result}! \\ $$