How to integrate e$^{int}$ with respect to $t$?

Question

I am wanting to show that $\int_{0}^{2\pi}e^{nit}dt=0$ for $n\neq0$, but I am unsure if it is correct to write $$\int_{0}^{2\pi}e^{int}\mathrm dt=\left.\frac{e^{int}}{ni}\right|_{0}^{2\pi}$$ or $$\int_{0}^{2\pi}e^{int}\mathrm dt=\left.\frac{e^{int}}{n}\right|_{0}^{2\pi}$$

I know both will yield the same answer but it will help to know for future reference.

Your first integration is correct, because you are working in the $t$ $world$. So here $i$ and $n$ are treated to be constants. — Jimmy, Mar 25 '19 at 12:03

score 4 · Accepted Answer · edited Mar 25 '19 at 12:35

4

The first one is correct; the second one is not. The formula arises from the fact that $\frac d {dt} e^{int}=ine^{int}$.

edited Mar 25 '19 at 12:35

J. W. Tanner

60,406

answered Mar 25 '19 at 11:59

Kavi Rama Murthy

311,013

score 1 · Answer 2 · answered Mar 25 '19 at 12:14

1

Set $ni=k$, then you have: $$\int_0^{2\pi}e^{kt}dt=\bigg(\frac{e^{kt}}{k}\bigg)^{2\pi}_0$$

answered Mar 25 '19 at 12:14

Rhys Hughes

12,842

score 0 · Answer 3 · edited Mar 25 '19 at 12:35

0

The first is correct; $\mathrm i$ is a constant too (so it has to be in the antiderivative).

edited Mar 25 '19 at 12:35

J. W. Tanner

60,406

answered Mar 25 '19 at 11:59

log_math

2,401

How to integrate e$^{int}$ with respect to $t$?

3 Answers3