Energy of a complex exponential I want to obtain the energy of this signal $$x_i(t)= e^{j2\pi(2i-1)f_0t}$$ where $f_0 = 1$ Hz, $i= 1,...,4$ and $j$ is a complex. I think I need to use the Fourier transform or the Parseval theorem but I'm not sure how to apply it.
As mentioned in the comments you can just take the integral of the squared magnitude.
Notice that the magnitude of $|e^{a+bj}| = |e^a||e^{bj}| = e^a$ for $a,b \in \mathbb{R}$, comparing with your function we see that $|x_i(t)|=1$. We conclude that $x_i(t)$ is a power signal, not an energy signal, i.e. you must define a time interval to integrate. Then the energy will be $\int_{t_0}^{t_f} |x_i(t)|^2  \mathrm{d}t = (t_f - t_0)$. I hope this helps.